Structures, acoustic wave resonators, devices and systems to sense a target variable

ABSTRACT

Techniques for improving Bulk Acoustic Wave (BAW) resonator structures are disclosed, including fluidic systems, oscillators and systems that may include such devices. A bulk acoustic wave (BAW) resonator may comprise a substrate and a first layer of piezoelectric material. The bulk acoustic wave (BAW) resonator may comprise a top electrode. A sensing region may be acoustically coupled with the top electrode of the bulk acoustic wave (BAW) resonator.

RELATED APPLICATIONS

This patent arises from a continuation of U.S. patent application Ser.No. 16/940,172 filed Jul. 27, 2020, entitled “STRUCTURES, ACOUSTIC WAVERESONATORS, DEVICES AND SYSTEMS TO SENSE A TARGET VARIABLE, INCLUDING ASA NON-LIMITING EXAMPLE CORONAVIRUSES”, which claims priority to thefollowing U.S. Provisional Patent Applications:

-   -   U.S. Provisional Patent Application Ser. No. 62/881,061,        entitled “BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES        AND SYSTEMS” and filed on Jul. 31, 2019;    -   U.S. Provisional Patent Application Ser. No. 62/881,074,        entitled “ACOUSTIC DEVICE STRUCTURES, DEVICES AND SYSTEMS” and        filed on Jul. 31, 2019;    -   U.S. Provisional Patent Application Ser. No. 62/881,077,        entitled “DOPED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES,        DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;    -   U.S. Provisional Patent Application Ser. No. 62/881,085,        entitled “BULK ACOUSTIC WAVE (BAW) RESONATOR WITH PATTERNED        LAYER STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31,        2019;    -   U.S. Provisional Patent Application Ser. No. 62/881,087,        entitled “BULK ACOUSTIC WAVE (BAW) REFLECTOR AND RESONATOR        STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;    -   U.S. Provisional Patent Application Ser. No. 62/881,091,        entitled “MASS LOADED BULK ACOUSTIC WAVE (BAW) RESONATOR        STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019; and    -   U.S. Provisional Patent Application Ser. No. 62/881,094,        entitled “TEMPERATURE COMPENSATING BULK ACOUSTIC WAVE (BAW)        RESONATOR STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31,        2019.    -   U.S. patent application Ser. No. 16/940,172 and each of the        provisional patent applications identified above are        incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to acoustic resonators and to devices andto systems comprising acoustic resonators.

BACKGROUND

Viral infections represent a grave threat to public health as well asthe global economy. Viral infections may occur through contaminatedwater, food, and/or bodily fluids, spread rapidly, and result in deathof humans and animals worldwide. Significant concerns have been raiseddue to recent Coronavirus (e.g., SARS CoV-2 virus) outbreaks, since theCoronavirus spreads very quickly and caused the ongoing COVID-19 globalpandemic. For example, as many as 10 million cases or more of COVID-19may have been reported in more than 188 countries and territories. Thismay have resulted in more than 500,000 deaths, and may have caused thelargest global recession since the Great Depression.

Rapid and accurate detection can mean the difference between life anddeath during viral infections. Historically, viral detection processeshave been slow and expensive, in part because remote laboratories waitedto receive bodily fluid samples collected from patients for analysis todetermine whether a small number viral particles indicating an incipientinfection may be present, and to determine whether antibodies generatedby the patient immune response against the virus indicating an advancedinfection may be present. Laboratory methods such as virus culture,enzyme-linked immunosorbent assay (ELISA), western blots, andserological antibody detection methods are prone to error, especially indetermining whether a small number viral particles indicating anincipient infection may be present. Traditional laboratory-based assaysare also time-consuming, labor-intensive, expensive, and can be in somecases relatively insensitive, and in all cases require samples to betransported to centralized diagnostic laboratories for testing.Expensive laboratory tools are difficult to transport, too difficult touse, and too slow for use where they are most needed: at the point ofpatient care. These factors increase time-to-answer and costs whilereducing the quality of patient care. In the case of Coronavirus, theworld has seen first hand the consequences of high diagnostic testingprices, the lack of diagnostic test availability, and delayed andinaccurate determinations, as Coronavirus has spread through subsequentcontacts of patients unaware that they are infected.

Exacerbating the difficulties in detecting a single virus is itsinfinitesimally small size and weight. A single virus may be so small inmagnitude that it may weigh only one femtogram in air. Examples of thisscale are seen in two raisins weighing a gram, an average human cellbeing one trillion times smaller in magnitude at one nanogram. At onefemtogram, a single virus may be a million times smaller in magnitudethan the average human sell. Making matters slightly worse, a virus mayhave some buoyancy and may weigh less as collected in a liquid sample,e.g., a virus may weight ten times less in water, e.g., weigh a mere 100attograms in water.

The future of public health and the global economy may very well dependon innovation of new technologies to detect things that are very small,in ways that are inexpensive, quick, accurate, and easy to performon-site where they are needed. Like viruses, toxic levels of lead indrinking water in Flint, Michigan can be accurately diagnosed at remotelaboratories (e.g., using X ray diffraction analysis), but laboratoryequipment (e.g., X ray diffraction equipment) may be too expensive, toodifficult to transport, too difficult to use, and too slow for use whereit is needed most, at the point where the Flint community consumes theirwater. Moreover, brave soldiers in the field or stationed at remotebases may face threats from airborne biological weapon attacks, chemicalweapon attacks, radiation and the like. Quick and accurate diagnostictesting is needed in the field for these soldiers, rather than requiringthem to wait for delayed results processed at remote laboratories. Evenordinary civilians may need government protection from terroristattacks, which could be preventable in advance by early field detectionof miniscule quantities of explosives, chemicals associated withchemical weapons, or toxins in the civilian water supply.

While conventional ELISAs in remote laboratories can measure picomolarconcentrations of analytes, higher sensitivities may be required becauseeven a few molecules of toxins can be harmful, individual pathogens caninitiate an infectious disease, and trace amounts of a cancer biomarkercan indicate the beginning of a malignant transformation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows simplified diagrams of a bulk acoustic wave resonatorstructure of and its operation in a thickness extensional main resonantmode.

FIG. 1A is a diagram that illustrates an example bulk acoustic waveresonator structure.

FIG. 1B is a simplified view of FIG. 1A that illustrates acoustic stressprofile during electrical operation of the bulk acoustic wave resonatorstructure shown in FIG. 1A.

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure corresponding to the cross sectional view of FIG.1A, and also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure.

FIG. 1D is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingreverse axis orientation of negative polarization.

FIG. 1E is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingnormal axis orientation of positive polarization.

FIGS. 2A and 2B show a further simplified view of a bulk acoustic waveresonator similar to the bulk acoustic wave resonator structure shown inFIG. 1A along with its corresponding impedance versus frequency responseduring its electrical operation, as well as alternative bulk acousticwave resonator structures with differing numbers of alternating axispiezoelectric layers, and their respective corresponding impedanceversus frequency response during electrical operation, as predicted bysimulation.

FIG. 2C shows additional alternative bulk acoustic wave resonatorstructures with additional numbers of alternating axis piezoelectriclayers.

FIGS. 2D and 2E show more additional alternative bulk acoustic waveresonator structures.

FIGS. 3A through 3C illustrate example integrated circuit structuresused to form the example bulk acoustic wave resonator structure of FIG.1A. Note that although AlN is used as an example piezoelectric layermaterial, the present disclosure is not intended to be so limited. Forexample, in some embodiments, the piezoelectric layer material mayinclude other group III material-nitride (III-N) compounds (e.g., anycombination of one or more of gallium, indium, and aluminum withnitrogen), and further, any of the foregoing may include doping, forexample, of Scandium, Magnesium, Hafnium, Magnesium-Zirconium and/orMagnesium-Niobium doping.

FIGS. 4A through 4C show alternative example bulk acoustic waveresonators to the example bulk acoustic wave resonator structures shownin FIG. 1A.

FIG. 5 shows a simplified top view of an example fluidic system of thisdisclosure, along with a simplified cross sectional view of the fluidicsystem showing operation of an example bulk acoustic wave resonatorstructure and sensing region of this disclosure.

FIGS. 6A through 6C are simplified diagrams of various exampleresonators of this disclosure, along with respective diagramsillustrating respective corresponding properties as predicted bysimulation.

FIGS. 7A and 7B are simplified diagrams of various additional exampleresonators of this disclosure, along with respective diagramsillustrating respective corresponding properties as predicted bysimulation.

FIG. 8A shows an example oscillator using the bulk acoustic waveresonator structure of FIG. 1A sensing in liquid.

FIG. 8B shows a schematic of and example circuit implementation of theoscillator shown in FIG. 8A.

FIG. 8C shows an array of eighteen Smith charts showing Scatteringparameters (S-parameters) at various operating frequencies correspondingvarious example BAW resonators having from one to six piezoelectriclayers in alternating piezoelectric axis stack arrangements, and havingtop electrodes thickness varying from about a tenth of the acousticwavelength of the BAW resonators to one half of the acoustic wavelengthof the BAW resonators, to one acoustic wavelength of the BAW resonators.

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example bulk acoustic wave resonators shown in FIG. 1A, FIGS. 2Athrough 2E, and FIGS. 4A through 4C, the example fluidic system of FIG.5 , and the example oscillators shown in FIGS. 8A and 8B.

FIG. 9C shows a simplified system employing an array of BAW resonatorstructures for sensing according to this disclosure.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices using the techniques disclosed herein, inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Non-limiting embodiments will be described by way of example withreference to the accompanying figures, which are schematic and are notintended to be drawn to scale. In the figures, each identical or nearlyidentical component illustrated is typically represented by a singlenumeral. For purposes of clarity, not every component is labeled inevery figure, nor is every component of each embodiment shown whereillustration is not necessary to allow understanding by those ofordinary skill in the art. In the specification, as well as in theclaims, all transitional phrases such as “comprising,” “including,”“carrying,” “having,” “containing,” “involving,” “holding,” “composedof,” and the like are to be understood to be open-ended, i.e., to meanincluding but not limited to. Only the transitional phrases “consistingof” and “consisting essentially of” shall be closed or semi-closedtransitional phrases, respectively. Further, relative terms, such as“above,” “below,” “top,” “bottom,” “upper” and “lower” are used todescribe the various elements' relationships to one another, asillustrated in the accompanying drawings. It is understood that theserelative terms are intended to encompass different orientations of thedevice and/or elements in addition to the orientation depicted in thedrawings. For example, if the device were inverted with respect to theview in the drawings, an element described as “above” another element,for example, would now be below that element. The term “compensating” isto be understood as including “substantially compensating”. The terms“oppose”, “opposes” and “opposing” are to be understood as including“substantially oppose”, “substantially opposes” and “substantiallyopposing” respectively. Further, as used in the specification andappended claims, and in addition to their ordinary meanings, the terms“substantial” or “substantially” mean to within acceptable limits ordegree. For example, “substantially canceled” means that one skilled inthe art would consider the cancellation to be acceptable. As used in thespecification and the appended claims and in addition to its ordinarymeaning, the term “approximately” or “about” means to within anacceptable limit or amount to one of ordinary skill in the art. Forexample, “approximately the same” means that one of ordinary skill inthe art would consider the items being compared to be the same. As usedin the specification and appended claims, the terms “a”, “an” and “the”include both singular and plural referents, unless the context clearlydictates otherwise. Thus, for example, “a device” includes one deviceand plural devices. As used herein, the International TelecommunicationUnion (ITU) defines Super High Frequency (SHF) as extending betweenthree Gigahertz (3 GHz) and thirty Gigahertz (30 GHz). The ITU definesExtremely High Frequency (EHF) as extending between thirty Gigahertz (30GHz) and three hundred Gigahertz (300 GHz).

FIG. 1 shows simplified diagrams of a bulk acoustic wave resonatorstructure of this disclosure and its operation in a thicknessextensional main resonant mode. Bulk acoustic wave resonator structures1000A, 1000B, 1000C may include respective multilayer metal acousticreflector electrodes 1013A, 1013B, 1013C arranged over respectivesubstrates 1001A, 1001B, 1001C (e.g., silicon substrate 1001A, 1001B,1001C), and respective harmonically tuned top electrode top sensorelectrodes 1015A, 1015B, 1015C acoustically coupled with respectivesensing regions 1016A, 1016B, 1016C. In a non-limiting example, bulkacoustic wave resonator structures 1000A, 1000B, 1000C may operate withtheir respective sensing regions 1016A, 1016B, 1016C to sense an analyte(e.g., coronavirus, e.g., SARS CoV-2 virus) in a fluid 1018A, 1018B,1018C, e.g., liquid 1018A, 1018B, 1018C, e.g., comprising water.Harmonically tuned top sensor electrodes 1015A, 1015B, 1015C may haverespective thicknesses that are approximately an integral multiple of ahalf of an acoustic wavelength of the respective resonant frequencies ofthe BAW resonators coupled with respective sensing regions 1016A, 1016B,1016C. The harmonically tuned top sensor electrodes 1015A, 1015B, 1015Cmay facilitate suppressing parasitic lateral modes. Respective stacks ofpiezoelectric material layers (e.g., stacks of normal axis piezoelectriclayer 1005A, 1005B, 1005C and reverse axis piezoelectric layer 1007A,1007B, 1007C) may be respectively sandwiched between respectivemultilayer metal acoustic reflector electrodes 1013A, 1013B, 1013C andrespective harmonically tuned top electrode top sensor electrodes 1015A,1015B, 1015C.

For example, in FIG. 1 , respective acoustic reflectors 1013A, 1013B,1013C (e.g., respective acoustic reflector electrodes 1013A, 1013B,1013C) may be respective multi-layer acoustic reflectors 1013A, 1013B,1013C (e.g., may be respective multi-layer acoustic reflector electrodes1013A, 1013B, 1013C). For example, respective multi-layer acousticreflectors 1013A, 1013B, 1013C (e.g., respective multi-layer acousticreflector electrodes 1013A, 1013B, 1013C) may approximate respectivedistributed Bragg reflectors 1013A, 1013B, 1013C. For example,respective multi-layer acoustic reflectors 1013A, 1013B, 1013C (e.g.,respective multi-layer acoustic reflector electrodes 1013A, 1013B,1013C) may include respective acoustic layers 1013A, 1013B, 1013C (e.g.,respective first pairs of bottom metal electrode layers 1022A, 1022B,1022C). For example, respective layers of respective multi-layeracoustic reflectors 1013A, 1013B, 1013C may be respectively arranged inrespective alternating arrangements of low acoustic impedance metallayers and high acoustic impedance metal layers.

For example, in FIG. 1 , respective acoustic reflectors 1013A, 1015A,1013B, 1015B (e.g., respective acoustic reflector electrodes 1013A,1015A, 1013B, 1015B) may be acoustically tuned approximately forrespective resonant frequencies of the respective BAW resonators 1000A,1000B, 1000C. For example, respective acoustic reflectors 1013A, 1013B,1013C (e.g., respective acoustic reflector electrodes 1013A, 1013B,1013C) may approximate respective distributed Bragg reflectors 1013A,1013B, 1013C, having respective quarter wavelength resonances which maybe acoustically tuned approximately for respective resonant frequenciesof the respective BAW resonators 1000A, 1000B, 1000C. For example,respective acoustic layers (e.g., first pair of bottom acoustic layers1022A, 1022B, 1022C) of the respective multi-layer acoustic reflectors1013A, 1013B, 1013C may have respective layer thicknesses selected sothat the respective multi-layer acoustic reflectors 1013A, 1013B, 1013C,may have respective quarter wavelength resonances at respectivefrequencies that may be acoustically tuned approximately for therespective resonant frequencies of the respective BAW resonators 1000A,1000B, 1000C. For example, respective metal electrode layers (e.g.,first pair of bottom metal electrode layers 1022A, 1022B, 1022C) of therespective tuned multi-layer metal reflector electrodes 1013A, 1013B,1013C, may have respective layer thicknesses selected so that therespective tuned multi-layer acoustic reflectors 1013A, 1013B, 1013C,may have respective quarter wavelength resonances at respectivefrequencies that may be acoustically tuned for approximately therespective resonant frequencies of the respective BAW resonators 1000A,1000B, 1000C.

The stacks of piezoelectric material layers (e.g., stacks of normal axispiezoelectric layer 1005A, 1005B, 1005C and reverse axis piezoelectriclayer 1007A, 1007B, 1007C) may have respective active regions whereharmonically tuned top electrode top sensor electrodes 1015A, 1015B,1015C may respectively overlap respective multilayer metal acousticreflector electrodes 1013A, 1013B, 1013C. For example, in operation ofBAW resonators 1000A, 1000B, 1000C an oscillating electric field may beapplied via harmonically tuned top electrode top sensor electrodes1015A, 1015B, 1015C and respective multilayer metal acoustic reflectorelectrodes 1013A, 1013B, 1013C, so as to activate responsivepiezoelectric acoustic oscillations in a thickness extensional mainresonant mode in the respective active regions of the stacks ofpiezoelectric material layers (e.g., stacks of normal axis piezoelectriclayer 1005A, 1005B, 1005C and reverse axis piezoelectric layer 1007A,1007B, 1007C), where harmonically tuned top electrode top sensorelectrodes 1015A, 1015B, 1015C may respectively overlap respectivemultilayer metal acoustic reflector electrodes 1013A, 1013B, 1013C.

For illustrative purposes, bulk acoustic resonator 1000A depictsapproximately equal half acoustic wavelength thicknesses of normal axispiezoelectric layer 1005A and reverse axis piezoelectric layer 1007A,for example, prior to activation of the thickness extensional mainresonant mode by application of the oscillating electric field viaharmonically tuned top electrode top sensor electrode 1015A andmultilayer metal acoustic reflector electrode. In contrast, bulkacoustic resonators 1000B, 1000C depict thickness changes in normal axispiezoelectric layers 1005B, 1005C and reverse axis piezoelectric layers1007B, 1007C from activation of the thickness extensional main resonantmode by application of the oscillating electric field via harmonicallytuned top electrode top sensor electrodes 1015B, 1015C and multilayermetal acoustic reflector electrodes 1013B, 1013C.

As illustrated in BAW resonator 1000B, during an initial half cycle ofthe thickness extensional main resonant mode, normal axis piezoelectriclayer 1005B is in extension and while reverse axis piezoelectric layer1007B is in compression. The extension is representatively illustratedby a thickened depiction of normal axis piezoelectric layer 1005B (e.g.,relative to unactivated normal axis piezoelectric layer 1005A). Thecompression is representatively illustrated by a thinned depiction ofreverse axis piezoelectric layer 1007B (e.g., relative to unactivatedreverse axis piezoelectric layer 1007A). A dashed line at the interfacebetween normal axis piezoelectric layer 1005B and reverse axispiezoelectric layer 1007B is used to depict motion of thicknessextensional main resonant mode.

As illustrated in BAW resonator 1000C, during a subsequent half cycle ofthe thickness extensional main resonant mode, normal axis piezoelectriclayer 1005C is in compression and while reverse axis piezoelectric layer1007C is in extension. The compression is representatively illustratedby a thinned depiction of normal axis piezoelectric layer 1005C (e.g.,relative to unactivated normal axis piezoelectric layer 1005A). Theextension is representatively illustrated by a thickened depiction ofreverse axis piezoelectric layer 1007C (e.g., relative to unactivatedreverse axis piezoelectric layer 1007A). A dashed line at the interfacebetween normal axis piezoelectric layer 1005C and reverse axispiezoelectric layer 1007C is used to depict motion of the thicknessextensional main resonant mode. For illustrative purposes in depictionsof BAW resonators 1000B, 1000C, amounts of extension (thickening) andcompression (thinning) are greatly exaggerated.

The thickness extensional main resonant mode depicted in FIG. 1 is alongitudinal mode excited in a vertically grown piezoelectric materialfilm by coupling a vertically applied electric field through a d33piezoelectric coefficient. The main thickness extensional resonance modeof BAW resonators of this disclosure may offer the highest sensitivityto analytes, for example, using sensing regions 1016A, 1016B, 1016Cshown in FIG. 1 . For example, both the acoustic wave velocity andresonance frequency of the thickness extensional main resonant mode ofthe BAW resonators of this disclosure are higher than acoustic wavevelocity and resonance frequency of shear mode resonators and may offerhigher sensitivity to analytes than shear mode resonators. BAWresonators of this disclosure may have sensing regions (e.g., sensingregions 1016A, 1016B, 1016C), which may comprise a respectivefunctionalized layers (not shown in the simplified view of FIG. 1 ). Thefunctionalized layers of the sensing regions (e.g., sensing regions1016A, 1016B, 1016C) may be used to selectively bind and detectbiomolecules (e.g., coronavirus, e.g., SARS CoV-2). Such selectivebinding and detection may occur in real time or near real time. BAWresonators of this disclosure may use a resonance frequency shift (adecrease in resonance frequency) that may be caused by the mass ofbiomolecules selectively binding with the functionalized layer. Thistechnique need not require fluorescent tags or chemical labels fordetection of biomolecules.

Further, mass sensitivity may increase with the square of frequency. Thethickness extensional main resonant mode BAW resonators of thisdisclosure may operate with resonant frequencies in the Super HighFrequency band (e.g., main resonant frequency of 24.25 GHz, or higherbands, e.g., higher main resonant frequencies), and so their masssensitivity may be much higher than resonators operating below the SuperHigh Frequency band. Thus, label-free, highly sensitive and selective,and real-time detection of biomolecules (e.g., coronavirus, e.g., SARSCoV-2) may, but need not be achieved by BAW resonators of thisdisclosure.

For example, respective harmonically tuned top electrode top sensorelectrodes 1015A, 1015B, 1015C and respective multilayer metal acousticreflector electrodes 1013A, 1013B, 1013C may be respectively coupled(e.g., electrically coupled, e.g., acoustically coupled) with therespective normal axis piezoelectric layers 1005A, 1005B, 1005C and thereverse axis piezoelectric layers 1007A, 1007B, 1007C to excite thepiezoelectrically excitable resonance mode (e.g., thickness extensionalmain resonant mode) at respective resonant frequencies of the bulkacoustic Super High Frequency (SHF) wave resonators 1000A, 1000B, 1000Cin the Super High Frequency (SHF) wave band (e.g., 24.25 GHz mainresonant frequency). For example, thicknesses of the normal axispiezoelectric layers 1005A, 1005B, 1005C and the reverse axispiezoelectric layers 1007A, 1007B, 1007C may be selected to determinethe main resonant frequency of bulk acoustic Super High Frequency (SHF)wave resonators 1000A, 1000B, 1000C in the Super High Frequency (SHF)wave band (e.g., twenty-four and a quarter GigaHertz, 24.25 GHz mainresonant frequency).

Further, quality factor (Q factor) is a figure of merit for bulkacoustic wave resonators that may be related, in part, to acousticreflector electrode conductivity. In accordance with the teachings ofthis disclosure, without an offsetting compensation that increasesnumber of member layers, member layer thinning with increasing frequencymay otherwise diminish acoustic reflector electrode conductivity, andmay otherwise diminish quality factor (Q factor) of bulk acoustic waveresonators. In accordance with the teachings of this disclosure, numberof member layers of the multilayer metal acoustic reflector electrodes1013A, 1013B, 1013C may be increased in designs extending to higherresonant frequencies, to facilitate electrical conductivity throughacoustic reflector electrodes. The acoustic reflector electrodes (e.g.,Super High Frequency (SHF) bottom acoustic reflector electrode 1013A,1013B, 1013C may have sheet resistance of less than one Ohm per squareat the given frequency (e.g., at the main resonant frequency of the BAWresonator in the super high frequency band or the extremely highfrequency band, e.g., at the quarter wavelength resonant frequency ofthe acoustic reflector electrode in the super high frequency band or theextremely high frequency band). For example, a sufficient number ofmember layers may be employed to provide for this sheet resistance atthe given frequency (e.g., at the main resonant frequency of the BAWresonator in the super high frequency band or the extremely highfrequency band, e.g., at the quarter wavelength resonant frequency ofthe acoustic reflector electrode in the super high frequency band or theextremely high frequency band). This may, but need not, facilitateenhancing quality factor (Q factor) to a quality factor (Q factor) thatis above a desired value of one hundred (100).

Moreover, quality factor (Q factor) may, but need not be increased bythe inclusion of reverse axis piezoelectric layer 1007A, 1007B, 1007C inacoustic coupling with normal axis piezoelectric layer 1005A, 1005B,1005C. In accordance with the teachings of this disclosure, without anoffsetting compensation that increases number of member piezoelectriclayers in an alternating piezoelectric axis arrangement, memberpiezoelectric layer thinning with increasing frequency may otherwisediminish quality factor (Q factor) of bulk acoustic wave resonators. Inaccordance with the teachings of this disclosure, number of memberpiezoelectric layers in an alternating piezoelectric axis arrangementmay be increased in designs extending to higher resonant frequencies.This may, but need not boost quality factor (Q factor). Furthermore,higher Q factor may, but need not increase detection sensitivity (e.g.,sensitivity in detection of biomolecules, e.g., sensitivity in detectionof coronavirus.)

FIG. 1A is a diagram that illustrates an example bulk acoustic waveresonator structure 100. FIGS. 4A through 4C show alternative examplebulk acoustic wave resonators, 400A through 400C, to the example bulkacoustic wave resonator structure 100 shown in FIG. 1A. The foregoingare shown in simplified cross sectional views. The resonator structuresare formed over a substrate 101, 401A through 401C (e.g., siliconsubstrate 101, 401A, 401B, e.g., silicon carbide substrate 401C). Insome examples, the substrate may further comprise a seed layer 103,403A, 403B, formed of, for example, aluminum nitride (AlN), or anothersuitable material (e.g., silicon dioxide (SiO₂), aluminum oxide (Al₂O₃),silicon nitride (Si₃N₄), amorphous silicon (a-Si), silicon carbide(SiC)), having an example thickness in a range from approximately 100 Ato approximately 1 um on the silicon substrate. In some other examples,the seed layer 103, 403A, 403B may also be at least partially formed ofelectrical conductivity enhancing material such as Aluminum (Al) or Gold(Au).

The example resonators 100, 400A through 400C, include a respectivestack 104, 404A through 404C, of an example four layers of piezoelectricmaterial, for example, four layers of Aluminum Nitride (AlN) having awurtzite structure. For example, FIG. 1A and FIGS. 4A through 4C show abottom piezoelectric layer 105, 405A through 405C, a first middlepiezoelectric layer 107, 407A through 407C, a second middlepiezoelectric layer 109, 409A through 409C, and a top piezoelectriclayer 111, 411A through 411C. A mesa structure 104, 404A through 404C(e.g., first mesa structure 104, 404A through 404C) may comprise therespective stack 104, 404A through 404C, of the example four layers ofpiezoelectric material. The mesa structure 104, 404A through 404C (e.g.,first mesa structure 104, 404A through 404C) may comprise bottompiezoelectric layer 105, 405A through 405C. The mesa structure 104, 404Athrough 404C (e.g., first mesa structure 104, 404A through 404C) maycomprise first middle piezoelectric layer 107, 407A through 407C. Themesa structure 104, 404A through 404C (e.g., first mesa structure 104,404A through 404C) may comprise second middle piezoelectric layer 109,409A through 409C. The mesa structure 104, 404A through 404C (e.g.,first mesa structure 104, 404A through 404C) may comprise toppiezoelectric layer 111, 411A through 411C. Although piezoelectricaluminum nitride may be used, alternative examples may comprisealternative piezoelectric materials, e.g., doped aluminum nitride, e.g.,zinc oxide, e.g., lithium niobate, e.g., lithium tantalate.

The four layers of piezoelectric material in the respective stack 104,404A through 404C of FIG. 1A and FIGS. 4A through 4C may have analternating axis arrangement in the respective stack 104, 404A through404C. For example the bottom piezoelectric layer 105, 405A through 405Cmay have a normal axis orientation, which is depicted in the figuresusing a downward directed arrow. Next in the alternating axisarrangement of the respective stack 104, 404A through 404C, the firstmiddle piezoelectric layer 107, 407A through 407C may have a reverseaxis orientation, which is depicted in the figures using an upwarddirected arrow. Next in the alternating axis arrangement of therespective stack 104, 404A through 404C, the second middle piezoelectriclayer 109, 409A through 409C may have the normal axis orientation, whichis depicted in the figures using the downward directed arrow. Next inthe alternating axis arrangement of the respective stack 104, 404Athrough 404C, the top piezoelectric layer 111, 411A through 411C mayhave the reverse axis orientation, which is depicted in the figuresusing the upward directed arrow.

For example, polycrystalline thin film MN may be grown in acrystallographic c-axis negative polarization, or normal axisorientation perpendicular relative to the substrate surface usingreactive magnetron sputtering of an Aluminum target in a nitrogenatmosphere. However, as will be discussed in greater detail subsequentlyherein, changing sputtering conditions, for example by adding oxygen,may reverse the axis to a crystallographic c-axis positive polarization,or reverse axis, orientation perpendicular relative to the substratesurface.

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, the bottom piezoelectric layer 105, 405A through 405C,may have a piezoelectrically excitable resonance mode (e.g., mainresonance mode, e.g., thickness extensional main resonance mode) at aresonant frequency (e.g., main resonant frequency) of the exampleresonators. Similarly, the first middle piezoelectric layer 107, 407Athrough 407C, may have its piezoelectrically excitable resonance mode(e.g., main resonance mode, e.g., thickness extensional main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators. Similarly, the second middle piezoelectric layer109, 409A through 409C, may have its piezoelectrically excitableresonance mode (e.g., main resonance mode, e.g., thickness extensionalmain resonance mode) at the resonant frequency (e.g., main resonantfrequency) of the example resonators. Similarly, the top piezoelectriclayer 111, 411A through 411C, may have its piezoelectrically excitablemain resonance mode (e.g., main resonance mode, e.g., thicknessextensional main resonance mode) at the resonant frequency (e.g., mainresonant frequency) of the example resonators. Accordingly, the toppiezoelectric layer 111, 411A through 411C, may have itspiezoelectrically excitable main resonance mode (e.g., main resonancemode, e.g., thickness extensional main resonance mode) at the resonantfrequency (e.g., main resonant frequency) with the bottom piezoelectriclayer 105, 405A through 405C, the first middle piezoelectric layer 107,407A through 407C, and the second middle piezoelectric layer 109, 409Athrough 409C.

The bottom piezoelectric layer 105, 405A through 405C, may beacoustically coupled with the first middle piezoelectric layer 107, 407Athrough 407C, in the piezoelectrically excitable resonance mode (e.g.,main resonance mode, e.g., thickness extensional main resonance mode) atthe resonant frequency (e.g., main resonant frequency) of the exampleresonators 100, 400A through 400C. The normal axis of bottompiezoelectric layer 105, 405A through 405C, in opposing the reverse axisof the first middle piezoelectric layer 107, 407A through 407C, maycooperate for the piezoelectrically excitable resonance mode (e.g., mainresonance mode, e.g., thickness extensional main resonance mode) at theresonant frequency (e.g., main resonant frequency) of the exampleresonators. The first middle piezoelectric layer 107, 407A through 407C,may be sandwiched between the bottom piezoelectric layer 105, 405Athrough 405C, and the second middle piezoelectric layer 109, 409Athrough 409C, for example, in the alternating axis arrangement in therespective stack 104, 404A through 404C. For example, the reverse axisof the first middle piezoelectric layer 107, 407A through 407C, mayoppose the normal axis of the bottom piezoelectric layer 105, 405Athrough 405C, and the normal axis of the second middle piezoelectriclayer 109, 409A-409C. In opposing the normal axis of the bottompiezoelectric layer 105, 405A through 405C, and the normal axis of thesecond middle piezoelectric layer 109, 409A through 409C, the reverseaxis of the first middle piezoelectric layer 107, 407A through 407C, maycooperate for the piezoelectrically excitable resonance mode (e.g., mainresonance mode, e.g., thickness extensional main resonance mode) at theresonant frequency (e.g., main resonant frequency) of the exampleresonators.

The second middle piezoelectric layer 109, 409A through 409C, may besandwiched between the first middle piezoelectric layer 107, 407Athrough 407C, and the top piezoelectric layer 111, 411A through 411C,for example, in the alternating axis arrangement in the respective stack104, 404A through 404C. For example, the normal axis of the secondmiddle piezoelectric layer 109, 409A through 409C, may oppose thereverse axis of the first middle piezoelectric layer 107, 407A through407C, and the reverse axis of the top piezoelectric layer 111, 411Athrough 411C. In opposing the reverse axis of the first middlepiezoelectric layer 107, 407A through 407C, and the reverse axis of thetop piezoelectric layer 111, 411A through 411C, the normal axis of thesecond middle piezoelectric layer 109, 409A through 409C, may cooperatefor the piezoelectrically excitable resonance mode (e.g., main resonancemode, e.g., thickness extensional main resonance mode) at the resonantfrequency (e.g., main resonant frequency) of the example resonators.Similarly, the alternating axis arrangement of the bottom piezoelectriclayer 105, 405A through 405C, and the first middle piezoelectric layer107, 407A through 407C, and the second middle piezoelectric layer 109,409A through 409C, and the top piezoelectric layer 111, 411A through411C, in the respective stack 104, 404A through 404C may cooperate forthe piezoelectrically excitable resonance mode (e.g., main resonancemode, e.g., thickness extensional main resonance mode) at the resonantfrequency (e.g., main resonant frequency) of the example resonators.Despite differing in their alternating axis arrangement in therespective stack 104, 404A through 404C, the bottom piezoelectric layer105, 405A through 405C and the first middle piezoelectric layer 107,407A through 407C, and the second middle piezoelectric layer 109, 409Athrough 409C, and the top piezoelectric layer 111, 411A through 411C,may all be made of the same piezoelectric material, e.g., AluminumNitride (AlN).

Respective layers of piezoelectric material in the stack 104, 404Athrough 404C, of FIG. 1A and FIGS. 4A through 4C may have respectivelayer thicknesses of about one half wavelength (e.g., one half acousticwavelength) of the main resonant frequency of the example resonators.For example, respective layers of piezoelectric material in the stack104, 404A through 404C, of FIG. 1A and FIGS. 4A through 4C may haverespective layer thicknesses so that (e.g., selected so that) therespective bulk acoustic wave resonators 100, 400A through 400C may haverespective resonant frequencies that are in a Super High Frequency (SHF)band or an Extremely High Frequency (EHF) band (e.g., respectiveresonant frequencies that are in a Super High Frequency (SHF) band,e.g., respective resonant frequencies that are in an Extremely HighFrequency (EHF) band. For example, respective layers of piezoelectricmaterial in the stack 104, 404A through 404C, of FIG. 1A and FIGS. 4Athrough 4C may have respective layer thicknesses so that (e.g., selectedso that) the respective bulk acoustic wave resonators 100, 400A through400C may have respective resonant frequencies that are in a millimeterwave band. For example, for an approximately twenty-four gigahertz(e.g., 24 GHz) main resonant frequency of the example resonators, thebottom piezoelectric layer 105, 405A through 405C, may have a layerthickness corresponding to about one half of a wavelength (e.g., aboutone half of an acoustic wavelength) of the main resonant frequency, andmay be about two thousand Angstroms (2000 A). Similarly, the firstmiddle piezoelectric layer 107, 407A through 407C, may have a layerthickness corresponding the one half of the wavelength (e.g., one halfof the acoustic wavelength) of the main resonant frequency; the secondmiddle piezoelectric layer 109, 409A through 409C, may have a layerthickness corresponding the one half of the wavelength (e.g., one halfof the acoustic wavelength) of the main resonant frequency; and the toppiezoelectric layer 111, 411A through 411C, may have a layer thicknesscorresponding the one half of the wavelength (e.g., one half of theacoustic wavelength) of the main resonant frequency. Piezoelectric layerthickness may be scaled up or down to determine main resonant frequency.

The example resonators 100, 400A through 400C, of FIG. 1A and FIGS. 4Athrough 4C may comprise: a bottom acoustic reflector 113, 413A through413C (e.g., multi-layer bottom acoustic reflector 113, 413A through413C, e.g., multi-layer metal bottom acoustic reflector electrode 113,413A through 413C), e.g., including an acoustically reflective bottomelectrode stack of a plurality of bottom metal electrode layers; and aharmonically tuned top sensor electrode 115, 415A through 415C.Accordingly, the bottom acoustic reflector 113, 413A through 413C, maybe a bottom multi-layer acoustic reflector. The piezoelectric layerstack 104, 404A through 404C, may be sandwiched between the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413C, and the top metal electrode layer of the harmonicallytuned top sensor electrode 115, 415A through 415C. Harmonically tunedtop sensor electrode 115, 415A through 415C may comprise the relativelyhigh acoustic impedance metal, for example, Tungsten, Ruthenium orMolybdenum. In other examples, harmonically tuned top sensor electrode115, 415A through 415C may comprise (at least partially) a relativelylarge electrical conductivity material, for example, Aluminum or Gold.The piezoelectric layer stack 104, 404A through 404C, may beelectrically and acoustically coupled with the plurality of bottom metalelectrode layers of the bottom acoustic reflector 113, 413A through 413Cand the top metal electrode layer of the harmonically tuned top sensorelectrode 115, 415A through 415C, to excite the piezoelectricallyexcitable resonance mode (e.g., main resonance mode, e.g., thicknessextensional main resonance mode) at the resonant frequency (e.g., mainresonant frequency). For example, such excitation may be done by usingthe plurality of bottom metal electrode layers of the bottom acousticreflector 113, 413A through 413C and the top metal electrode layer ofthe harmonically tuned top sensor electrode 115, 415A through 415C toapply an oscillating electric field having a frequency corresponding tothe resonant frequency (e.g., main resonant frequency) of thepiezoelectric layer stack 104, 404A through 404C, and of the exampleresonators 100, 400A through 400C. For example, the piezoelectric layerstack 104, 404A through 404C, may be electrically and acousticallycoupled with the plurality of bottom metal electrode layers of thebottom acoustic reflector 113, 413A through 413C and the top metalelectrode layer of the harmonically tuned top sensor electrode 115, 415Athrough 415C, to excite the piezoelectrically excitable resonance mode(e.g., main resonance mode, e.g., thickness extensional main resonancemode) at the resonant frequency (e.g., main resonant frequency).

For example, the bottom piezoelectric layer 105, 405A through 405C, maybe electrically and acoustically coupled with the plurality of bottommetal electrode layers of the bottom acoustic reflector 113, 413Athrough 413C and the top metal electrode layer of the harmonically tunedtop sensor electrode 115, 415A through 415C, to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode,e.g., thickness extensional main resonance mode) at the resonantfrequency (e.g., main resonant frequency) of the bottom piezoelectriclayer 105, 405A through 405C. Further, the bottom piezoelectric layer105, 405A through 405C and the first middle piezoelectric layer 107,407A through 407C, may be electrically and acoustically coupled with theplurality of bottom metal electrode layers of the bottom acousticreflector 113, 413A through 413C, and the top metal electrode layer ofthe harmonically tuned top sensor electrode 115, 415A through 415C, toexcite the piezoelectrically excitable resonance mode (e.g., mainresonance mode, e.g., thickness extensional main resonance mode) at theresonant frequency (e.g., main resonant frequency) of the bottompiezoelectric layer 105, 405A through 405C, acoustically coupled withthe first middle piezoelectric layer 107, 407A through 407C.Additionally, the first middle piezoelectric layer 107, 407A through407G, may be sandwiched between the bottom piezoelectric layer 105, 405Athrough 405C and the second middle piezoelectric layer 109, 409A through409C, and may be electrically and acoustically coupled with theplurality of bottom metal electrode layers of the bottom acousticreflector 113, 413A through 413C, and the top metal electrode layer ofthe harmonically tuned top sensor electrode 115, 415A through 415C, toexcite the piezoelectrically excitable resonance mode (e.g., mainresonance mode, e.g., thickness extensional main resonance mode) at theresonant frequency (e.g., main resonant frequency) of the first middlepiezoelectric layer 107, 407A through 407C, sandwiched between thebottom piezoelectric layer 105, 405A through 405C, and the second middlepiezoelectric layer 109, 409A through 409C.

The acoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413C, may have an alternating arrangement of low acousticimpedance metal layer and high acoustic impedance metal layer. Theacoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413C may approximate a distributed Bragg acoustic reflector,e.g. a metal distributed Bragg acoustic reflector. The plurality ofmetal bottom electrode layers of the bottom acoustic reflector may beelectrically coupled (e.g., electrically interconnected) with oneanother. The acoustically reflective bottom electrode stack of theplurality of bottom metal electrode layers may operate together as amulti-layer (e.g., bi-layer, e.g., multiple layer) bottom electrode forthe bottom acoustic reflector 113, 413A through 413C.

In the alternating arrangement of low acoustic impedance metal layer andhigh acoustic impedance metal layer of the acoustically reflectivebottom electrode stack, may be a first pair of bottom metal electrodelayers 119, 419A through 419C and 121, 421A through 421C. A first member119, 419A through 419C, of the first pair of bottom metal electrodelayers may comprise a relatively low acoustic impedance metal, forexample, Titanium having an acoustic impedance of about 27 MegaRayls, orfor example, Aluminum having an acoustic impedance of about 18MegaRayls. A second member 121, 421A through 421C, of the first pair ofbottom metal electrode layers may comprise the relatively high acousticimpedance metal, for example, Tungsten or Molybdenum. Accordingly, thefirst pair of bottom metal electrode layers 119, 419A through 419C, and121, 421A through 421C, of the bottom acoustic reflector 113, 413Athrough 413C, may be different metals, and may have respective acousticimpedances that are different from one another so as to provide areflective acoustic impedance mismatch at the resonant frequency (e.g.,main resonant frequency). Similarly, the first member of the first pairof bottom metal electrode layers 119, 419A through 419C, of the bottomacoustic reflector 113, 413A through 413C, may be different metals, andmay have respective acoustic impedances that are different from oneanother so as to provide a reflective acoustic impedance mismatch at theresonant frequency (e.g., main resonant frequency).

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a second pair of bottom metalelectrode layers 123, 423A through 423C, and 125, 425A through 425C, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Accordingly, members ofthe first and second pairs of bottom metal electrode layers 119, 419Athrough 419C, 121, 421A through 421C, 123, 423A through 423C, 125, 425Athrough 425C, may have respective acoustic impedances in the alternatingarrangement to provide a corresponding plurality of reflective acousticimpedance mismatches.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a third pair of bottom metalelectrode layers 127, 129 may respectively comprise the relatively lowacoustic impedance metal and the relatively high acoustic impedancemetal. Next in the alternating arrangement of low acoustic impedancemetal layer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a fourth pair of bottom metalelectrode layers 131, 133 may respectively comprise the relatively lowacoustic impedance metal and the relatively high acoustic impedancemetal.

Respective thicknesses of the bottom metal electrode layers may berelated to wavelength (e.g., acoustic wavelength) for the main resonantfrequency of the example bulk acoustic wave resonators, 100, 400Athrough 400C. Further, various embodiments for resonators havingrelatively higher resonant frequency (higher main resonant frequency)may have relatively thinner bottom metal electrode thicknesses, e.g.,scaled thinner with relatively higher resonant frequency (e.g., highermain resonant frequency). Similarly, various alternative embodiments forresonators having relatively lower resonant frequency (e.g., lower mainresonant frequency) may have relatively thicker bottom metal electrodelayer thicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency).

Further, the bottom acoustic reflectors 113, 413A through 413C may beacoustically de-tuned from respective resonant frequencies of therespective BAW resonators 100, 400A through 400C. For example,respective multi-layer bottom acoustic reflectors 113, 413A through 413C(e.g., respective multi-layer bottom acoustic reflector electrodes 113,413A through 413C, e.g., respective multi-layer metal bottom acousticreflector electrodes 113, 413A through 413C) may approximate respectivedistributed Bragg reflectors 113, 413A through 413C, (e.g., respectivemetal distributed Bragg reflectors 113, 413A through 413C), which may beacoustically de-tuned from respective resonant frequencies of therespective BAW resonators 100, 400A through 400C. For example,respective bottom acoustic layers of the respective de-tuned multi-layerbottom acoustic reflectors 113, 413A through 413C may have respectivelayer thicknesses selected so that the respective de-tuned multi-layeracoustic reflectors 113, 413A through 413C may have respective quarterwavelength resonant frequencies that may be acoustically de-tuned fromthe respective resonant frequencies of the respective BAW resonators100, 400A through 400C. For example, bottom metal electrode layers(e.g., first pair of bottom metal electrode layers 119, 419A through419C, 121, 421A through 421C, e.g., second pair of bottom metalelectrode layers 123, 423A through 423C, 125, 425A through 425C, e.g.,third pair of bottom metal electrode layers 127, 129, fourth pair ofbottom metal electrode layers 131, 133) may have respective layerthicknesses selected so that the respective de-tuned multi-layeracoustic reflectors 113, 413A through 413C may have respective quarterwavelength resonant frequencies that may be acoustically de-tuned to bebelow the respective resonant frequencies of the respective BAWresonators 100, 400A through 400C. For example, for a 24 GHz resonator,(e.g., resonator having a main resonant frequency of about 24 GHz)bottom metal electrode layers may have respective layer thicknessesselected so that the respective de-tuned multi-layer bottom acousticreflectors 113, 413A through 413C may have respective quarter wavelengthresonant frequencies that may be acoustically de-tuned to be below(e.g., 2 GHz below) the respective resonant frequencies of therespective BAW resonators 100, 400A through 400C, e.g., acousticallyde-tuned to about 22 GHz. As will be discussed in greater detailsubsequently herein, bottom acoustic reflector de-tuning may facilitatesuppressing parasitic (e.g., undesired) lateral resonances in acousticresonators, for example, in respective BAW resonators 100, 400A through400C.

In various differing examples, multi-layer bottom acoustic reflectors(e.g., the multi-layer bottom acoustic reflectors 113, 413A through413C) may be de-tuned (e.g. tuned down in frequency) by variousdiffering amounts from the resonant frequency (e.g. main resonantfrequency) of the BAW resonator. As discussed in greater detailsubsequently herein, in examples having about one or two piezoelectriclayers in an alternating piezoelectric axis stack arrangement, thede-tuned multi-layer bottom acoustic reflector (e.g., the multi-layermetal bottom acoustic reflector electrode) may be acoustically de-tuned(e.g. tuned down in frequency) from the resonant frequency (e.g. mainresonant frequency) of the BAW resonator.

For example in the figures, the first member of the first pair of bottommetal electrode layers 119, 419A through 419C, of the bottom acousticreflector 113, 413A through 413C, is depicted as relatively thicker(e.g., thickness T01 of the first member of the first pair of bottommetal electrode layers 119, 419A through 419C is depicted as relativelythicker) than thickness of remainder bottom acoustic layers (e.g., thanthicknesses T02 through T08 of remainder bottom metal electrode layers).For example, a thickness T01 may be about 9% greater, e.g.,substantially greater, than an odd multiple (e.g., 1×, 3×, etc.) of aquarter of a wavelength (e.g., 9% greater than one quarter of theacoustic wavelength) for the first member of the first pair of bottommetal electrode layers 119, 419A through 419C. For example, if Titaniumis used as the low acoustic impedance metal for a 24 GHz resonator(e.g., resonator having a main resonant frequency of about 24 GHz), athickness T01 may be about 690 Angstroms, 690 A, for the first member ofthe first pair of bottom metal electrode layers 119, 419A through 419C,of the bottom acoustic reflector 113, 413A through 413C, whilerespective layer thicknesses, T02 through T08, shown in the figures forcorresponding members of the pairs of bottom metal electrode layers maybe substantially thinner than T01.

Respective layer thicknesses, T02 through T08, shown in FIG. 1A forcorresponding members of the pairs of bottom metal electrode layers maybe about an odd multiple (e.g., 1×, 3×, etc.) of a quarter of awavelength (e.g., one quarter of the acoustic wavelength) at the mainresonant frequency of the example resonator. However, the foregoing maybe varied. For example, members of the pairs of bottom metal electrodelayers of the bottom acoustic reflector may have respective layerthickness that are within a range from about one eighth to about onehalf wavelength at the resonant frequency, or an odd multiple (e.g., 1×,3×, etc.) thereof.

In an example, if Tungsten is used as the high acoustic impedance metal,and the main resonant frequency of the resonator is approximatelytwenty-four gigahertz (e.g., 24 GHz), then using the one quarter of thewavelength (e.g., one quarter of the acoustic wavelength) provides thelayer thickness of the high impedance metal electrode layer members ofthe pairs as about five hundred and forty Angstroms (540 A). Forexample, if Titanium is used as the low acoustic impedance metal, andthe main resonant frequency of the resonator is approximatelytwenty-four gigahertz (e.g., 24 GHz), then using the one quarter of thewavelength (e.g., one quarter of the acoustic wavelength) provides thelayer thickness of the low impedance metal electrode layer members ofthe second, third and fourth pairs as about six hundred and thirtyAngstroms (630 A). Similarly, respective layer thicknesses for membersof the remainder pairs of bottom metal electrode layers shown in FIGS.4A through 4C (e.g., second, third and fourth pairs) may likewise beabout one quarter of the wavelength (e.g., one quarter of the acousticwavelength) of the main resonant frequency of the example resonator, andthese respective layer thicknesses may likewise be determined formembers of the pairs of bottom metal electrode layers for the high andlow acoustic impedance metals employed.

As shown in the figures, a second member 121, 421A through 421C of thefirst pair of bottom metal electrode layers may have a relatively highacoustic impedance (e.g., high acoustic impedance metal layer 121, 421Athrough 421C, e.g. tungsten metal layer 121, 421A through 421C). A firstmember 119, 419A through 419C of the first pair of bottom metalelectrode layers may have a relatively low acoustic impedance (e.g., lowacoustic impedance metal layer 119, 419A through 419C, e.g., titaniummetal layer 119, 419A through 419C). This relatively low acousticimpedance of the first member 119, 419A through 419C of the first pairmay be relatively lower than the acoustic impedance of the second member121, 421A through 421C of the first pair. The first member 119, 419Athrough 419C having the relatively lower acoustic impedance may abut alayer of piezoelectric material (e.g. may abut bottom piezoelectriclayer 105, 405A through 405C, e.g. may abut piezoelectric stack 104,404A through 404C). This arrangement may facilitate suppressingparasitic lateral resonances in operation of the BAW resonator. Thefirst member 119, 419A through 419C having the relatively lower acousticimpedance may be arranged nearest to a layer of piezoelectric material(e.g. may be arranged nearest to bottom piezoelectric layer 105, 405Athrough 405C, e.g. may be arranged nearest to piezoelectric stack 104,404A through 404C) relative to other bottom acoustic layers of thebottom acoustic reflector 113, 413A through 413C (e.g. relative to thesecond member 121, 421A through 421C of the first pair of bottom metalelectrode layers, the second pair of bottom metal electrode layers 123,423A through 423C, 125, 425A through 425C, the third pair of bottommetal electrode layers 127, 427A through 427C, 129, 429A through 429C,and the fourth pair of bottom metal electrodes 131, 431A through 431C,133, 433A through 433C). This arrangement may facilitate suppressingparasitic lateral resonances in operation of the BAW resonator.

The first member 119, 419A through 419C having the relatively loweracoustic impedance may be arranged sufficiently proximate to the a layerof piezoelectric material (e.g. may be arranged sufficiently proximateto bottom piezoelectric layer 105, 405A through 405C, e.g. may bearranged sufficiently proximate to piezoelectric stack 104, 404A through404C), so that the first member 119, 419A through 419C having therelatively lower acoustic impedance may contribute more to themulti-layer metal bottom acoustic reflector electrode 113, 413A through413C being acoustically de-tuned from the resonant frequency of the BAWresonator than is contributed by any other bottom metal electrode layerof the multi-layer metal bottom acoustic reflector electrode 113, 413Athrough 413C (e.g., contribute more than the second member 121, 421Athrough 421C of the first pair of bottom metal electrode layers, e.g.,contribute more than the first member 123, 423A through 423C of thesecond pair of bottom metal electrode layers, e.g., contribute more thanthe second member 125, 425A through 425C of the second pair of bottommetal electrode layers, e.g., contribute more than the first member 127,427A through 427C of the third pair of bottom metal electrode layers,e.g., contribute more than the second member 129, 429A through 429C ofthe third pair of bottom metal electrode layers, e.g., contribute morethan the first member 131, 431A through 431C of the fourth pair ofbottom metal electrodes, e.g., contribute more than the second member133, 433A through 433C of the fourth pair of bottom metal electrodes).The first member 119, 419A through 419C having the relatively loweracoustic impedance may be arranged sufficiently proximate to the a layerof piezoelectric material (e.g. may be arranged sufficiently proximateto bottom piezoelectric layer 105, 405A through 405C, e.g. may bearranged sufficiently proximate to piezoelectric stack 104, 404A through404C), so that the first member 119, 419A through 419C having therelatively lower acoustic impedance may contribute more to facilitatesuppressing parasitic lateral resonances in operation of the BAWresonator than is contributed by any other bottom metal electrode layerof the multi-layer metal bottom acoustic reflector electrode 113, 413Athrough 413C (e.g., contribute more than the second member 121, 421Athrough 421C of the first pair of bottom metal electrode layers, e.g.,contribute more than the first member 123, 423A through 423C of thesecond pair of bottom metal electrode layers, e.g., contribute more thanthe second member 125, 425A through 425C of the second pair of bottommetal electrode layers, e.g., contribute more than the first member 127,427A through 427C of the third pair of bottom metal electrode layers,e.g., contribute more than the second member 129, 429A through 429C ofthe third pair of bottom metal electrode layers, e.g., contribute morethan the first member 131, 431A through 431C of the fourth pair ofbottom metal electrodes, e.g., contribute more than the second member133, 433A through 433C of the fourth pair of bottom metal electrodes).

For example, the bottom piezoelectric layer 105, 405A through 405C, maybe electrically and acoustically coupled with pair(s) of bottom metalelectrode layers (e.g., first pair of bottom metal electrode layers 119,419A through 419C, 121, 421A through 421C, e.g., second pair of bottommetal electrode layers 123, 423A through 423C, 125, 425A through 425C,e.g., third pair of bottom metal electrode layers 127, 129, fourth pairof bottom metal electrode layers 131, 133), to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode,e.g., thickness extensional main resonance mode) at the resonantfrequency (e.g., main resonant frequency) of the bottom piezoelectriclayer 105, 405A through 405C. Further, the bottom piezoelectric layer105, 405A through 405C and the first middle piezoelectric layer 107,407A through 407C may be electrically and acoustically coupled withpair(s) of bottom metal electrode layers (e.g., first pair of bottommetal electrode layers 119, 419A through 419C, 121, 421A through 421C,e.g., second pair of bottom metal electrode layers 123, 423A through423C, 125, 425A through 425C, e.g., third pair of bottom metal electrodelayers 127, 129), to excite the piezoelectrically excitable resonancemode (e.g., main resonance mode, e.g., thickness extensional mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the bottom piezoelectric layer 105, 405A through 405Cacoustically coupled with the first middle piezoelectric layer 107, 407Athrough 407C. Additionally, the first middle piezoelectric layer 107,407A through 407C, may be sandwiched between the bottom piezoelectriclayer 105, 405A through 405C, and the second middle piezoelectric layer109, 409A through 409C, and may be electrically and acoustically coupledwith pair(s) of bottom metal electrode layers (e.g., first pair ofbottom metal electrode layers 119, 419A through 419C, 121, 421A through421C, e.g., second pair of bottom metal electrode layers 123, 423Athrough 423C, 125, 425A through 425C, e.g., third pair of bottom metalelectrode layers 127, 129), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode, e.g., thickness extensionalmain resonance mode) at the resonant frequency (e.g., main resonantfrequency) of the first middle piezoelectric layer 107, 407A through407C, sandwiched between the bottom piezoelectric layer 105, 405Athrough 405C, and the second middle piezoelectric layer 109, 409Athrough 409C.

Another mesa structure 113, 413A through 413C, (e.g., second mesastructure 113, 413A through 413C), may comprise the bottom acousticreflector 113, 413A through 413C. The another mesa structure 113, 413Athrough 413C, (e.g., second mesa structure 113, 413A through 413C), maycomprise one or more pair(s) of bottom metal electrode layers (e.g.,first pair of bottom metal electrode layers 119, 419A through 419C, 121,421A through 421C, e.g., second pair of bottom metal electrode layers123, 423A through 423C, 125, 425A through 425C, e.g., third pair ofbottom metal electrode layers 127, 129, e.g., fourth pair of bottommetal electrode layers 131, 133).

Further, the respective harmonically tuned top sensor electrodes 115,415A through 415C may be acoustically de-tuned from respective resonantfrequencies of the respective BAW resonators 100, 400A through 400C. Forexample, respective harmonically tuned top sensor electrode 115, 415Athrough 415C (e.g., respective top acoustic electrodes 115, 415A through415C, e.g., respective metal top electrodes 115, 415A through 415C) maybe acoustically de-tuned from respective resonant frequencies of therespective BAW resonators 100, 400A through 400C. For example,respective de-tuned harmonically tuned top sensor electrodes 115, 415Athrough 415C may have respective metal electrode layer thicknessesselected so that the respective de-tuned harmonically tuned top sensorelectrodes 115, 415A through 415C may have respective half wavelengthresonant frequencies that may be acoustically de-tuned from therespective resonant frequencies of the respective BAW resonators 100,400A through 400C. For example, top metal electrode layers of de-tunedharmonically tuned top sensor electrodes 115, 415A through 415C may haverespective layer thicknesses selected so that the respective de-tunedharmonically tuned top sensor electrodes 115, 415A through 415C may haverespective half wavelength resonant frequencies that may be acousticallyde-tuned to be above the respective resonant frequencies of therespective BAW resonators 100, 400A through 400C. For example, for a 24GHz resonator, (e.g., resonator having a main resonant frequency ofabout 24 GHz) top metal electrode layers may have respective layerthicknesses selected so that the respective de-tuned harmonically tunedtop sensor electrodes 115, 415A through 415C may have respective halfwavelength resonance frequencies that may be acoustically de-tuned to beabove (e.g., 2 GHz above) the respective resonant frequencies of therespective BAW resonators 100, 400A through 400C, e.g., acousticallyde-tuned to about 26 GHz. As will be discussed in greater detailsubsequently herein, top acoustic reflector de-tuning may facilitatesuppressing parasitic (e.g., undesired) lateral resonances in acousticresonators, for example, in respective BAW resonators 100, 400A through400C.

In various differing examples, de-tuned harmonically tuned top sensorelectrodes 115, 415A through 415C may be de-tuned (e.g., tuned up infrequency) by various differing amounts from the resonant frequency(e.g. main resonant frequency) of the BAW resonator. As discussed ingreater detail subsequently herein, in examples having about one or twopiezoelectric layers in an alternating piezoelectric axis stackarrangement, the de-tuned harmonically tuned top sensor electrodes 115,415A through 415C may be acoustically de-tuned (e.g., tuned up infrequency) from the resonant frequency (e.g. main resonant frequency) ofthe BAW resonator by about up to about 5% of the resonant frequency(e.g. main resonant frequency) of the BAW resonator. It is theorizedthat this de-tuning by up to about 5% may facilitate suppression ofparasitic lateral resonances for resonators comprising about one or twopiezoelectric layers. In examples having about three piezoelectriclayers to about six piezoelectric layers in an alternating piezoelectricaxis stack arrangement, de-tuned harmonically tuned top sensorelectrodes 115, 415A through 415C may be acoustically de-tuned (e.g.,tuned up in frequency) from the resonant frequency (e.g. main resonantfrequency) of the BAW resonator by up to about 12% of the resonantfrequency (e.g. main resonant frequency) of the BAW resonator. It istheorized that this de-tuning by up to about 12% may facilitatesuppression of parasitic lateral resonances for resonators comprisingthe about three piezoelectric layers to about six piezoelectric layers.In examples having about seven piezoelectric layers to about eighteenpiezoelectric layers, in an alternating piezoelectric axis stackarrangement, the de-tuned harmonically tuned top sensor electrodes 115,415A through 415C may be acoustically de-tuned (e.g., tuned up infrequency) from the resonant frequency (e.g. main resonant frequency) ofthe BAW resonator by up to about 36% of the resonant frequency (e.g.main resonant frequency) of the BAW resonator. It is theorized that thisde-tuning by up to about 36% may facilitate suppression of parasiticlateral resonances for resonators comprising the about sevenpiezoelectric layers to about eighteen piezoelectric layers. In exampleshaving greater than about eighteen piezoelectric layers, in analternating piezoelectric stack arrangement, the de-tuned harmonicallytuned top sensor electrodes 115, 415A through 415C may be acousticallyde-tuned (e.g., tuned up in frequency) from the resonant frequency (e.g.main resonant frequency) of the BAW resonator by greater than about 36%of the resonant frequency (e.g. main resonant frequency) of the BAWresonator. It is theorized that this de-tuning by greater than 36% mayfacilitate suppression of parasitic lateral resonances for resonatorscomprising greater than eighteen piezoelectric layers.

Respective thicknesses of the de-tuned harmonically tuned top sensorelectrodes 115, 415A through 415C may be related to wavelength (e.g.,acoustic wavelength) for the main resonant frequency of the example bulkacoustic wave resonators, 100, 400A through 400C. Further, variousembodiments for resonators having relatively higher main resonantfrequency may have relatively thinner harmonically tuned top sensorelectrode thicknesses, e.g., scaled thinner with relatively higher mainresonant frequency. Similarly, various alternative embodiments forresonators having relatively lower main resonant frequency may haverelatively thicker harmonically tuned top sensor electrode thicknesses,e.g., scaled thicker with relatively lower main resonant frequency.

In an example, if Molybdenum is used as the high acoustic impedancemetal, and the main resonant frequency of the resonator is approximatelytwenty-four gigahertz (e.g., 24 GHz), then using the half wavelength(e.g., half acoustic wavelength) may provide the layer thickness of thehigh impedance metal of the harmonically tuned top sensor electrodes asabout one thousand three hundred Angstroms (1300 A). The bottom acousticreflector 113, 413A through 413C, may have a thickness dimension T23extending along the stack of bottom electrode layers. For the example ofthe 24 GHz resonator, the thickness dimension T23 of the bottom acousticreflector may be about five thousand Angstroms (5,000 A). Theharmonically tuned top sensor electrodes 115, 415A through 415C, mayhave a thickness dimension T25 extending along the harmonically tunedtop sensor electrodes. For the example of the 24 GHz resonator, thethickness dimension T25 of the harmonically tuned top sensor electrodes115, 415A through 415C may be about one thousand three hundred Angstroms(1300 A). The piezoelectric layer stack 104, 404A through 404C, may havea thickness dimension T27 extending along the piezoelectric layer stack104, 404A through 404C. For the example of the 24 GHz resonator, thethickness dimension T27 of the piezoelectric layer stack may be abouteight thousand Angstroms (8,000 A).

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, a notional heavy dashed line is used in depicting anetched edge region 153, 453A through 453C, associated with the exampleresonators 100, 400A through 400C. Similarly, a laterally opposingetched edge region 154, 454A through 454C is arranged laterally opposingor opposite from the notional heavy dashed line depicting the etchededge region 153, 453A through 453C. The etched edge region may, but neednot, assist with acoustic isolation of the resonators. The etched edgeregion may, but need not, help with avoiding acoustic losses for theresonators. The etched edge region 153, 453A through 453C, (and thelaterally opposing etched edge region 154, 454A through 454C) may extendalong the thickness dimension T27 of the piezoelectric layer stack 104,404A through 404C. The etched edge region 153, 453A through 453C, mayextend through (e.g., entirely through or partially through) thepiezoelectric layer stack 104, 404A through 404C. Similarly, thelaterally opposing etched edge region 154, 454A through 454C may extendthrough (e.g., entirely through or partially through) the piezoelectriclayer stack 104, 404A through 404C. The etched edge region 153, 453Athrough 453C, (and the laterally opposing etched edge region 154, 454Athrough 454C) may extend through (e.g., entirely through or partiallythrough) the bottom piezoelectric layer 105, 405A through 405C. Theetched edge region 153, 453A through 453C, (and the laterally opposingetched edge region 154, 454A through 454C) may extend through (e.g.,entirely through or partially through) the first middle piezoelectriclayer 107, 407A through 407C. The etched edge region 153, 453A through453C, (and the laterally opposing etched edge region 154, 454A through454C) may extend through (e.g., entirely through or partially through)the second middle piezoelectric layer 109, 409A through 409C. The etchededge region 153, 453A through 453C, (and the laterally opposing etchededge region 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the top piezoelectric layer 111, 411Athrough 411C.

The etched edge region 153, 453A through 453C, (and the laterallyopposing etched edge region 154, 454A through 454C) may extend along thethickness dimension T23 of the bottom acoustic reflector 113, 413Athrough 413C. The etched edge region 153, 453A through 453C, (and thelaterally opposing etched edge region 154, 454A through 454C) may extendthrough (e.g., entirely through or partially through) the bottomacoustic reflector 113, 413A through 413C. The etched edge region 153,453A through 453C, (and the laterally opposing etched edge region 154,454A through 454C) may extend through (e.g., entirely through orpartially through) the first pair of bottom metal electrode layers, 119,419A through 419C, 121, 421A through 421C. The etched edge region 153,453A through 453C (and the laterally opposing etched edge region 154,454A through 454C) may extend through (e.g., entirely through orpartially through) the second pair of bottom metal electrode layers,123, 423A through 423C, 125, 425A through 425C. The etched edge region153, 453A through 453C (and the laterally opposing etched edge region154, 454A through 454C) may extend through (e.g., entirely through orpartially through) the third pair of bottom metal electrode layers, 127,129. The etched edge region 153, 453A through 453C (and the laterallyopposing etched edge region 154, 454A through 454C) may extend through(e.g., entirely through or partially through) the fourth pair of bottommetal electrode layers, 131, 133.

The etched edge region 153, 453A through 453C (and the laterallyopposing etched edge region 154, 454A through 454C) may extend along thethickness dimension T25 of the harmonically tuned top sensor electrode115, 415A through 415C. The etched edge region 153, 453A through 453C(and the laterally opposing etched edge region 154, 454A through 454C)may extend through (e.g., entirely through or partially through) theharmonically tuned top sensor electrode 115, 415A through 415C.

The example resonators 100, 400A through 400C, of FIG. 1A and FIGS. 4Athrough 4C may include one or more (e.g., one or a plurality of)interposer layers sandwiched between piezoelectric layers of the stack104, 404A through 404C. For example, a first interposer layer 159, 459Athrough 459C may be sandwiched between the bottom piezoelectric layer105, 405A through 405C, and the first middle piezoelectric layer 107,407A through 407C. For example, a second interposer layer 161, 461Athrough 461C, may be sandwiched between the first middle piezoelectriclayer 107, 407A through 407C, and the second middle piezoelectric layer109, 409A through 409C. For example, a third interposer layer 163, 463Athrough 463C, may be sandwiched between the second middle piezoelectriclayer 109, 409A through 409C, and the top piezoelectric layer 111, 411Athrough 411C.

One or more (e.g., one or a plurality of) interposer layers may be metalinterposer layers. The metal interposer layers may be relatively highacoustic impedance metal interposer layers (e.g., using relatively highacoustic impedance metals such as Tungsten (W) or Molybdenum (Mo)). Suchmetal interposer layers may (but need not) flatten stress distributionacross adjacent piezoelectric layers and may (but need not) raiseeffective electromechanical coupling coefficient (Kt2) of adjacentpiezoelectric layers.

Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be dielectric interposer layers. The dielectric ofthe dielectric interposer layers may be a dielectric that has a positiveacoustic velocity temperature coefficient, so acoustic velocityincreases with increasing temperature of the dielectric. The dielectricof the dielectric interposer layers may be, for example, silicondioxide. Dielectric interposer layers may, but need not, facilitatecompensating for frequency response shifts with increasing temperature.Most materials (e.g., metals, e.g., dielectrics) generally have anegative acoustic velocity temperature coefficient, so acoustic velocitydecreases with increasing temperature of such materials. Accordingly,increasing device temperature generally causes response of resonatorsand filters to shift downward in frequency. Including dielectric (e.g.,silicon dioxide) that instead has a positive acoustic velocitytemperature coefficient may facilitate countering or compensating (e.g.,temperature compensating) this downward shift in frequency withincreasing temperature. Alternatively or additionally, one or more(e.g., one or a plurality of) interposer layers may comprise metal anddielectric for respective interposer layers. For example, high acousticimpedance metal layer such as Tungsten (W) Molybdenum (Mo) may (but neednot) raise effective electromechanical coupling coefficient (Kt2).Subsequently deposited amorphous dielectric layer such as SiliconDioxide (SiO2) may (but need not) facilitate compensating fortemperature dependent frequency shifts. Alternatively or additionally,one or more (e.g., one or a plurality of) interposer layers may comprisedifferent metals for respective interposer layers. For example, highacoustic impedance metal layer such as Tungsten (W), Molybdenum (Mo) may(but need not) raise effective electromechanical coupling coefficient(Kt2) while subsequently deposited metal layer with hexagonal symmetrysuch as Titanium (Ti) may (but need not) facilitate highercrystallographic quality of subsequently deposited piezoelectric layer.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may comprise different dielectrics for respectiveinterposer layers. For example, high acoustic impedance dielectric layersuch as Hafnium Dioxide (HfO2) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2). Subsequently depositedamorphous dielectric layer such as Silicon Dioxide (SiO2) may (but neednot) facilitate compensating for frequency dependent frequency shifts.

In addition to the foregoing application of metal interposer layers toraise effective electromechanical coupling coefficient (Kt2) of adjacentpiezoelectric layers, and the application of dielectric interposerlayers to facilitate compensating for frequency response shifts withincreasing temperature, interposer layers may, but need not, increasequality factor (Q-factor) and/or suppress irregular spectral responsepatterns characterized by sharp reductions in Q-factor known as“rattles”. Q-factor of a resonator is a figure of merit in whichincreased Q-factor indicates a lower rate of energy loss per cyclerelative to the stored energy of the resonator. Increased Q-factor inresonators used in filters results in lower insertion loss and sharperroll-off in filters. The irregular spectral response patternscharacterized by sharp reductions in Q-factor known as “rattles” maycause ripples in filter pass bands.

Metal and/or dielectric interposer layer of suitable thicknesses andacoustic material properties (e.g., velocity, density) may be placed atappropriate places in the stack 104, 404A through 404C, of piezoelectriclayers, for example, proximate to the nulls of acoustic energydistribution in the stacks (e.g., between interfaces of piezoelectriclayers of opposing axis orientation). Finite Element Modeling (FEM)simulations and varying parameters in fabrication prior to subsequenttesting may help to optimize interposer layer designs for the stack.Thickness of interposer layers may, but need not, be adjusted toinfluence increased Q-factor and/or rattle suppression. It is theorizedthat if the interposer layer is too thin there is no substantial effect.Thus minimum thickness for the interposer layer may be about onemono-layer, or about five Angstroms (5 A). Alternatively, if theinterposer layer is too thick, rattle strength may increase rather thanbeing suppressed. Accordingly, an upper limit of interposer thicknessmay be about five-hundred Angstroms (500 A) for an approximatelytwenty-four gigahertz (24 GHz) resonator design, with limiting thicknessscaling inversely with frequency for alternative resonator designs. Itis theorized that below a series resonant frequency of resonators, Fs,Q-factor may not be systematically and significantly affected byincluding a single interposer layer. However, it is theorized that theremay, but need not, be significant increases in Q-factor for inclusion oftwo or more interposer layers.

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, a planarization layer 165, 465A through 465C (e.g.,passivation layer 165, 465A through 465C) may be included. A suitablematerial may be used for planarization layer 165, 465A through 465C, forexample Silicon Dioxide (SiO2), Hafnium Dioxide (HfO2), polyimide, orBenzoCyclobutene (BCB). An isolation layer 167, 467A through 467C, mayalso be included and arranged over the planarization layer 165,465A-465C. For the acoustic resonator based sensor of this disclosure, asuitable dielectric material may be used for the isolation layer 167,467A through 467C, for example Silicon Nitride, Silicon Dioxide, orAluminum Nitride. Thickness of isolation layer 167, 467A through 467Cmay be controlled, for example, to be very thin. For example, thicknessof isolation layer 167, 467A through 467C may be within a range fromapproximately fifty Angstroms to approximately three hundred Angstroms(approximately 50 A to approximately 300 A) for resonators designed tooperate at approximately 24 GHz.

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, a bottom electrical interconnect 169, 469A through 469C,may be included to interconnect electrically with (e.g., electricallycontact with) the bottom acoustic reflector 113, 413A through 413C,stack of the plurality of bottom metal electrode layers. A topelectrical interconnect 171, 471A through 471C, may be included tointerconnect electrically with the harmonically tuned top sensorelectrode 115, 415A through 415C. A suitable material may be used forthe bottom electrical interconnect 169, 469A through 469C, and the topelectrical interconnect 171, 471A through 471C, for example, gold (Au).Top electrical interconnect 171, 471A through 471C may be arrangedsubstantially away from an active area of the stack 104, 404A through404C of the example four layers of piezoelectric material. This mayprovide for top electrical interconnect 171, 471A through 471C beingsubstantially acoustically isolated from the active area of the stack104, 404A through 404C of the example four layers of piezoelectricmaterial. Top electrical interconnect 171, 471A through 471C may havedimensions selected so that the top electrical interconnect 171, 471Athrough 471C approximates an electrical transmission line impedance atthe main resonant frequency of the bulk acoustic wave resonator 100,400A through 400C (e.g., in cases where the electrical impedance of thebulk acoustic wave resonator 100, 400A through 400C may be designed tobe near fifty ohms, the electrical transmission line impedance may beapproximately fifty ohms). Top electrical interconnect 171, 471A through471C may have a thickness that is substantially thicker than a thicknessthe harmonically tuned top sensor electrode 115, 415A through 415C. Topelectrical interconnect 171, 471A through 471C may have a thicknesswithin a range from about one hundred Angstroms (100 A) to about fivemicrometers (5 um). For example, top electrical interconnect 171, 471Athrough 471C may have a thickness of about two thousand Angstroms (2000A).

Bulk acoustic wave resonators 100, 400A through 400C may compriserespective sensing regions (e.g., sensing regions 116, 416A through416C). Sensing regions 116, 416A through 416C may comprise respectivefunctionalized layers 168, 468A through 468C. Respective functionalizedlayers 168, 468A through 468C may be patterned, e.g., may have theirlateral extents limited by patterning techniques, e.g., maskingtechniques, e.g., unmasked material removal techniques. Respectivefunctionalized layers 168, 468A through 468C may be patterned to bearranged over respective active regions of bulk acoustic wave resonators100, 400A through 400C (e.g., over central portions of the respectiveactive regions). Variations of functionalized layers 168, 468A through468C may be employed in combination with the other structures of bulkacoustic wave resonators 100, 400A through 400C for varied sensingpurposes. For example, respective functionalized layers 168, 468Athrough 468C may be different from one another. This may facilitaterespective responses (e.g., sensing responses) to differingenvironmental variables, e.g., binding to differing analytes. Respectivefunctionalized layers 168, 468A through 468C may facilitate binding torespective analytes. Respective functionalized layers 168, 468A through468C that may be different from one another to facilitate binding torespective analytes that may be different from one another. Respectivefunctionalized layers 168, 468A through 468C may be selected to haveaffinity (e.g., selective affinity) for one or more respective analytes(e.g., targeted analytes). For example, various functionalized layers168, 468A through 468C of the sensing regions (e.g., sensing regions116, 416A through 416C) may selectively bind to various analytes, e.g.,biomolecules (e.g., targeted biomolecules, e.g., coronavirus, e.g., SARSCoV-2, e.g., carriers of infectious disease, e.g., bioweapons, e.g.,biomarkers, e.g., targeted antigens, e.g., targeted antibodies), fordetection. For example, respective functionalized layers 168, 468Athrough 468C associated with bulk acoustic wave resonator 100, 400Athrough 400C may selectively bind the mass of one or more analytes,e.g., biomolecules (e.g., targeted biomolecules, e.g., coronavirus,e.g., SARS CoV-2, e.g., carriers of infectious disease, e.g.,bioweapons, e.g., biomarkers, e.g., targeted antigens, e.g., targetedantibodies), to the functionalized layers 168, 468A through 468C. Themass of one or more analytes, e.g., biomolecules (e.g., targetedbiomolecules, e.g., coronavirus, e.g., SARS CoV-2, e.g., carriers ofinfectious disease, e.g., bioweapons, e.g., biomarkers, e.g., targetedantigens, e.g., targeted antibodies), binding to the respectivefunctionalized layers 168, 468A through 468C may cause respectivedetectable resonance frequency shifts (e.g., decreases in respectiveresonance frequencies) in operation of bulk acoustic wave resonators100, 400A through 400C in their respective thickness extensional mainresonant modes. Respective electrical circuitry may be coupled with bulkacoustic wave resonators 100, 400A through 400C to determine theresonance frequency shifts. This may detect the presence of analytes,for example, biomolecules (e.g., targeted biomolecules, e.g.,coronavirus, e.g., SARS CoV-2, e.g., carriers of infectious disease,e.g., bioweapons, e.g., biomarkers, e.g., targeted antigens, e.g.,targeted antibodies).

Functionalized layers 168, 468A through 468C may comprise respectivebinding layers, e.g., respective layers of antibodies, e.g., respectivelayers of binding antibodies, e.g., receptors, e.g., ligands.Functionalized layers 168, 468A through 468C may comprise respectiveinterface layers (e.g., thin interface layers, e.g., very thin interfacelayers) e.g., of noble metal (e.g., gold). For example, the respectiveinterface layers, e.g., noble metal layers may be within a range fromfive Angstroms thick (e.g., approximately one monolayer) toapproximately one thousand five hundred Angstroms thick (e.g.,approximately one acoustic wavelength of thickness extensional mode atapproximately 24.25 GHz).

For functionalized layers 168, 468A through 468C, respective bindinglayers, e.g., respective layers of antibodies may be coupled with (e.g.,acoustically coupled with, e.g., may be arranged over) respectiveinterface layers (e.g., respective noble metal layers, e.g., respectivesupportive noble metal layers, e.g., respective noble metal layers).Functionalized layers 168, 468A through 468C may comprise respectiveimmobilization layers to couple respective binding layers (e.g.,respective layers of antibodies) to respective interface layers (e.g.,respective gold layers). Respective immobilization layers may bearranged over respective interface layers (e.g., respective goldlayers). Respective binding layers (e.g., respective layers ofantibodies) may be arranged over respective immobilization layers.Respective immobilization layers of functionalized layers 168, 468Athrough 468C may comprise respective “Protein A” layers, e.g.,respective immunoglobulin binding protein layers, to immobilizeantibodies on respective interface layers (e.g., to immobilizecoronavirus antibodies on respective gold interface layers, e.g., toimmobilize SARS Cov-2 antibodies on respective gold interface layers).

Respective immobilization layers of functionalized layers 168, 468Athrough 468C may comprise respective self assembled monolayers (e.g.,respective self assembled monolayers, e.g., self assembled monolayerscomprising thiol material). The respective binding layers, e.g.,respective layers of antibodies (e.g. respective layers of bindingantibodies) may be arranged over respective immobilization layers, e.g.,over respective self assembled monolayers. Respective self assembledmonolayers may be formed by exposure of respective interface layers tomolecules with chemical groups that exhibit strong affinities for therespective interface layers (e.g., strong affinities for respectivenoble metal layers, e.g., strong affinities for gold layers). Forexample, thiol-based (e.g., alkanethiol-based) assembled monolayers maybe used. For example, molecules like Alkanethiols may have e.g., analkyl chain as the back bone, may have e.g., a tail group, and may havee.g., a S—H head group. Thiols may be used on noble metal interfacelayers due to what may be a strong affinity for these metals. Examplesof thiol-based self assembly monolayers that may be used include mycomprise 1-dodecanethiol (DDT), 11-mercaptoundecanoic acid (MUA), andhydroxyl-terminated (hexaethylene glycol) undecanethiol (1-UDT). Thesethiols may contain the same or similar backbone, but different endgroups—namely, methyl (CH.sub.3), carboxyl (COOH), andhydroxyl-terminated hexaethylene glycol (HO—(CH.sub.2CH.sub.2O).sub.6)for DDT, MUA, and 1-UDT, respectively. Self assembly monolayers may beformed by incubating interface layers, e.g., noble metal layers, e.g.,gold layers, in thiol solutions using a suitable solvent, such asanhydrous ethanol. Following formation of respective self assembledmonolayers, the self assembled monolayers may be biologicallyfunctionalized, such as by receiving at least one functionalization(e.g., specific binding) material.

Examples of specific binding materials may include, but are not limitedto, antibodies, receptors, ligands, and the like. A specific bindingmaterial may be configured to receive a predefined target species (e.g.,molecule, protein, DNA, virus, bacteria, etc.) As another example,respective binding layers of respective functionalized layers 168, 468Athrough 468C may comprise aptamers, e.g., Prostate Specific Antigen(PSA) binding aptamers to bind with analyte biomarkers, e.g., ProstateSpecific Antigen (PSA) biomarkers, e.g., biomarkers for prostate cancer.As another example, respective binding layers of respectivefunctionalized layers 168, 468A through 468C may have an affinity forglucose (e.g., binding layers of (3-acrylamidopropyl) tri-methylammoniumchloride (poly(acrylamide-co-3-APB)). Glucose level may be recognized asa biomarker for management of diabetes.

More broadly, interactions of respective binding layers of respectivefunctionalized layers 168, 468A through 468C in pairings with analytesmay be viewed through the lens of biospecific interaction analysis (BIA)e.g., for antibody-antigen, e.g., for nucleic acids, e.g., for DNA-RNA,e.g., for protein-peptide, e.g. for enzymes-substrate, e.g., forreceptors-various molecules. Respective binding layers of respectivefunctionalized layers 168, 468A through 468C, may form one member ofthese pairings, and the other member may comprise the other member ofthese pairings. For example, as just discussed, respective bindinglayers of respective functionalized layers 168, 468A through 468C maycomprise antibodies (e.g., coronavirus antibodies) to detect an analyte,e.g., antigens (e.g., coronavirus antigens). However the roles may bereversed. Respective binding layers of respective functionalized layers168, 468A through 468C may comprise antigens (e.g., coronavirus antigensor portions thereof) to detect an analyte, e.g., antibodies (e.g.,coronavirus antibodies). The presence of antibodies (e.g., coronavirusantibodies) in a blood sample or a sputum sample collected from apatient may be indicative of an infection (e.g., COVID-19). Asadditional examples, respective binding layers of respectivefunctionalized layers 168, 468A through 468C may comprise a protein todetect an analyte, e.g., peptides. However the roles may be reversed.Respective binding layers of respective functionalized layers 168, 468Athrough 468C may comprise peptides to detect an analyte, e.g., proteins.

Respective members of respective functionalized layers 168, 468A through468C (e.g., respective antibody layers of respective functionalizedlayers 168, 468A through 468C, e.g., respective noble metal layers offunctionalized layers 168, 468A through 468C) may be coupled (e.g.,acoustically coupled) with other respective members of bulk acousticwave resonators 100, 400A through 400C (e.g., may be acousticallycoupled with respective isolation layers 167, 467A through 467C, e.g.,may be acoustically coupled with respective harmonically tuned topsensor electrodes 115, 415A through 415C, e.g., may be acousticallycoupled with respective stacks 104, 404A through 404C of alternatingaxis arrangements of piezoelectric layers, e.g., may be acousticallycoupled with respective bottom piezoelectric layers 105, 405A through405C (e.g., having a normal axis orientation), e.g., may be acousticallycoupled with respective first middle piezoelectric layers 107, 407Athrough 407C (e.g., having a reverse axis orientation), e.g., may beacoustically coupled with respective second middle piezoelectric layers109, 409A through 409C (e.g., having the normal axis orientation), e.g.,may be acoustically coupled with respective top piezoelectric layers111, 411A through 411C (e.g., having the reverse axis orientation)).

Respective targeted analytes (e.g., respective targeted biomolecules),in binding with respective layers of antibodies of functionalized layers168, 468A through 468C, may become acoustically coupled with respectivemembers of bulk acoustic wave resonators 100, 400A through 400C (e.g.,may become acoustically coupled with respective antibody layers ofrespective functionalized layers 168, 468A through 468C, e.g., maybecome acoustically coupled with respective noble metal layers offunctionalized layers 168, 468A through 468C e.g., may becomeacoustically coupled with respective isolation layers 167, 467A through467C, e.g., may become acoustically coupled with respective harmonicallytuned top sensor electrodes 115, 415A through 415C, e.g., may becomeacoustically coupled with respective stacks 104, 404A through 404C ofalternating axis arrangements of piezoelectric layers, e.g., may becomeacoustically coupled with respective bottom piezoelectric layers 105,405A through 405C (e.g., having a normal axis orientation), e.g., maybecome acoustically coupled with respective first middle piezoelectriclayers 107, 407A through 407C (e.g., having a reverse axis orientation),e.g., may become acoustically coupled with respective second middlepiezoelectric layers 109, 409A through 409C (e.g., having the normalaxis orientation), e.g., may become acoustically coupled with respectivetop piezoelectric layers 111, 411A through 411C (e.g., having thereverse axis orientation)).

Respective binding layers of functionalized layers 168, 468A through468C may comprise material (e.g., bacteria, e.g., Escherichia colibacteria) having an affinity for absorption of toxins, e.g., having anaffinity for absorption of heavy metals, e.g., having an affinity forabsorption of lead (Pb). Examples of heavy metals include mercury (Hg),cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl), and lead (Pb).As another example, respective binding layers of functionalized layers168, 468A through 468C may comprise material (e.g., cobalt corroles)having an affinity for absorption of toxins, e.g., having an affinityfor absorption of carbon monoxide. Functionalized layers 168, 468Athrough 468C may comprise respective nanoporous layers. In some cases,pore size of respective nanoporous layers may be tuned for analyteselectivity. Functionalized layers 168, 468A through 468C may compriserespective nanostructured layers. In some cases, nanostructure size ofrespective nanostructured layers may be tuned for analyte selectivity.

Respective binding layers of functionalized layers 168, 468A through468C may comprise materials having an affinity for volatile organiccompounds (e.g., hydrocarbons, e.g., alcohols, e.g., ammonia, e.g.,acetone, e.g., ketones, e.g., aldehydes, e.g., esters, e.g.,heterocycles). Example materials having affinity for volatile organiccompounds include, hexamethyldisiloxane (HMDSO), hexamethyldisilazane(HMDSN) and tetraethoxysilane (TEOS), polyaniline, calixarenes,chitosan, chitosan/polyaniline nanofibers, grapheme, molecularlyimprinted polymers, and mesoporous materials e.g., having a tunable porestructure.

Respective binding layers of functionalized layers 168, 468A through468C may comprise molecularly imprinted polymers, which may haveaffinity for one or more target analytes. In addition to affinity forvolatile organic compounds, as just mentioned, molecularly imprintedpolymers may be configured to have affinity for other analytes, e.g.,tetrahydrocannabinol (THC), e.g., biological weapons agents, e.g.,anthrax. Molecularly imprinted polymer may be configured to haveaffinity for explosives, e.g., trinitrotoluene (TNT), e.g.,1,3,5-trinitro-1,3,5-triazacyclohexane (RDX). Molecularly imprintedpolymers may be configured to have affinity for nerve agents, e.g.,Sarin. Molecularly imprinted polymers may be configured to have affinityfor a chemical associated with a chemical weapon, e.g., dimethylmethylphosphonate (DMMP). Dimethyl methylphosphonate (DMMP) isassociated with production of the Sarin nerve agent.

Respective functionalized layers 168, 468A through 468C may comprisenanocomposites. Respective functionalized layers 168, 468A through 468Cmay have an affinity for a chemical associated with a chemical weapon,e.g., dimethyl methylphosphonate (DMMP). For example, a nanocomposite ofZnO modified MnO2 nanofibers may have an affinity for dimethylmethylphosphonate (DMMP).

Numerous examples just discussed are directed to examples wherefunctionalized layers 168, 468A through 468C may include binding layers.Binding of analytes with functionalized layers 168, 468A through 468Cmay increase mass. This may lead to decrease in resonant frequency ofexample resonators 100, 400A through 400C. This may provide for analytedetection. In addition to the foregoing, there are the followingexamples of targeted energetic phenomena impinging on functionalizedlayers 168, 468A through 468C. Functionalized layers 168, 468A through468C may be selectively configured for targeted energetic phenomena.This may lead to increase in temperature of functionalized layers 168,468A through 468C. This may lead to decrease in resonant frequency ofexample resonators 100, 400A through 400C. This may provide fordetection of the targeted energetic phenomena.

For example, functionalized layers 168, 468A through 468C may comprise amaterial having an affinity for absorbing neutrons, e.g., a materialhaving a relatively high neutron cross section, e.g., cadmium. Forexample, respective functionalized layers 168, 468A through 468C maycomprise the material having the affinity for absorbing neutrons, e.g.,for absorbing the targeted energetic phenomena of a flux of thermalneutrons. This may lead to increase in temperature of functionalizedlayers 168, 468A through 468C. This may lead to decrease in resonantfrequency of example resonators 100, 400A through 400C. The flux ofthermal neutrons may be detected by example resonators 100, 400A through400C.

As another example, respective functionalized layers 168, 468A through468C may be selectively configured for a targeted energetic phenomena ofinfrared light. For example, respective functionalized layers 168, 468Athrough 468C may comprise material having an affinity for absorbinginfrared light, e.g., nanoplasmonic metasurfaces configured to absorbinfrared light. This may lead to increase in temperature offunctionalized layers 168, 468A through 468C. This may lead to decreasein resonant frequency of example resonators 100, 400A through 400C.Using the respective functionalized layers 168, 468A through 468C soconfigured, infrared light may be detected by example resonators 100,400A through 400C.

As another example, respective functionalized layers 168, 468A through468C may be selectively configured for a targeted energetic phenomena ofterahertz radiation. For example, respective functionalized layers 168,468A through 468C may comprise material having an affinity for absorbingterahertz radiation, e.g., nanoplasmonic metasurfaces configured toabsorb terahertz radiation. This may lead to increase in temperature offunctionalized layers 168, 468A through 468C. This may lead to decreasein resonant frequency of example resonators 100, 400A through 400C.Using the respective functionalized layers 168, 468A through 468C soconfigured, terahertz radiation may be detected by example resonators100, 400A through 400C.

As another example, respective functionalized layers 168, 468A through468C may be selectively configured for a targeted energetic phenomena ofsolar blind ultraviolet light. For example, respective functionalizedlayers 168, 468A through 468C may comprise material having an affinityfor absorbing solar blind ultraviolet light, e.g., beta gallium oxide(β-Ga2O3). This may lead to increase in temperature of functionalizedlayers 168, 468A through 468C. This may lead to decrease in resonantfrequency of example resonators 100, 400A through 400C. Using therespective functionalized layers 168, 468A through 468C so configured,solar blind ultraviolet light may be detected by example resonators 100,400A through 400C.

In addition to the forgoing examples, striction of respectivefunctionalized layers 168, 468A through 468C may be in response tosensed phenomena. This may cause a changed in resonant frequency ofexample resonators 100, 400A through 400C. This may provide fordetection of the sensed phenomena. For example, respectivefunctionalized layers 168, 468A through 468C may be magnetostrictive,e.g., striction of respective functionalized layers 168, 468A through468C may be in response to sensed magnetic phenomena. This may cause achange in resonant frequency of example resonators 100, 400A through400C, e.g., magnetic phenomena may be detected, e.g., changes inmagnetic phenomena may be detected. For example, respectivefunctionalized layers 168, 468A through 468C may comprise amagnetostrictive material. Respective functionalized layers 168, 468Athrough 468C may be multiferroic. Respective functionalized layers 168,468A through 468C may be magnetoelectric. Respective functionalizedlayers 168, 468A through 468C may comprise a nanocomposite. Respectivefunctionalized layers 168, 468A through 468C may comprise respectiveheterostructures. Respective functionalized layers 168, 468A through468C may comprise respective perovskite layers. Respectivefunctionalized layers 168, 468A through 468C may comprise respectivemagnetostrictive exchange biased multilayers. Respective functionalizedlayers 168, 468A through 468C may comprise respective antiparallelmagnetostrictive exchange biased multilayers.

More broadly, sensing regions 116, 416A through 416C may compriserespective functionalized layers 168, 468A through 468C. Sensing regions116, 416A through 416C may comprise at least respective portions ofrespective harmonically tuned top sensor electrodes 115, 415A through415C. Harmonically tuned top sensor electrodes 115, 415A through 415Cmay be magnetostrictive. Harmonically tuned top sensor electrodes 115,415A through 415C may comprise a magnetostrictive material. Respectivesensing regions 116, 416A through 416C may be acoustically coupled withrespective harmonically tuned top sensor electrodes 115, 415A through415C. This may comprise integral coupling of respective sensing regions116, 416A through 416C with respective harmonically tuned top sensorelectrodes 115, 415A through 415C. Respective sensing regions 116, 416Athrough 416C may comprise metallic glass (e.g., respectivefunctionalized layers 168, 468A through 468C may comprise metallicglass, e.g., harmonically tuned top sensor electrodes 115, 415A through415C may comprise metallic glass.) Respective sensing regions 116, 416Athrough 416C may comprise cobalt (e.g., respective functionalized layers168, 468A through 468C may comprise cobalt, e.g., harmonically tuned topsensor electrodes 115, 415A through 415C may comprise cobalt.)Respective sensing regions 116, 416A through 416C may comprise terbium(e.g., respective functionalized layers 168, 468A through 468C maycomprise terbium, e.g., harmonically tuned top sensor electrodes 115,415A through 415C may comprise terbium.) Respective sensing regions 116,416A through 416C may comprise samarium (e.g., respective functionalizedlayers 168, 468A through 468C may comprise samarium, e.g., harmonicallytuned top sensor electrodes 115, 415A through 415C may comprisesamarium.) Respective sensing regions 116, 416A through 416C maycomprise dysprosium (e.g., respective functionalized layers 168, 468Athrough 468C may comprise dysprosium, e.g., harmonically tuned topsensor electrodes 115, 415A through 415C may comprise dysprosium.)Respective sensing regions 116, 416A through 416C may comprise nickel(e.g., respective functionalized layers 168, 468A through 468C maycomprise nickel, e.g., harmonically tuned top sensor electrodes 115,415A through 415C may comprise nickel.) Respective sensing regions 116,416A through 416C may comprise a metallic alloy (e.g., respectivefunctionalized layers 168, 468A through 468C may comprise a metallicalloy, e.g., harmonically tuned top sensor electrodes 115, 415A through415C may comprise a metallic alloy.) Respective sensing regions 116,416A through 416C may comprise a giant magnetostrictive alloy (e.g.,respective functionalized layers 168, 468A through 468C may comprise agiant magnetostrictive alloy, e.g., harmonically tuned top sensorelectrodes 115, 415A through 415C may comprise a giant magnetostrictivealloy.)

Respective sensing regions 116, 416A through 416C may compriserespective tunable regions (e.g., respective functionalized layers 168,468A through 468C may comprise respective tunable regions, e.g.,harmonically tuned top sensor electrodes 115, 415A through 415C maycomprise tunable regions.) For example striction (e.g.,magnetostriction) may provide for tuning of resonant frequencies ofrespective resonators 100, 400A through 400C, in response to sensedphenomena (e.g., in response to magnetic phenomena). For example,respective bulk acoustic wave (BAW) resonators 100, 400A through 400Cmay comprise respective tunable bulk acoustic wave (BAW) resonators 100,400A through 400C. Respective bulk acoustic wave (BAW) resonators 100,400A through 400C may comprise at least a portion of a tunable electricfilter (e.g., ladder filter of interconnected tunable bulk acoustic wave(BAW) resonators).

FIG. 1B is a simplified view of FIG. 1A that illustrates an example ofacoustic stress distribution during electrical operation of the bulkacoustic wave resonator structure shown in FIG. 1A. A notional curvedline schematically depicts vertical (Tzz) stress distribution 173through stack 104 of the example four piezoelectric layers. The stress173 is excited by the oscillating electric field applied via theharmonically tuned top sensor electrode 115, and the multilayer metalacoustic reflector electrode 113 comprising bottom metal electrodelayers. The stress 173 has maximum values inside the stack 104 ofpiezoelectric layers, while exponentially tapering off within themultilayer metal acoustic reflector electrode 113. Acoustic energyconfined in the resonator structure 100 may be proportional to stressmagnitude.

As discussed previously herein, the example four piezoelectric layers inthe stack 104 may have an alternating axis arrangement in the stack 104.For example the bottom piezoelectric layer may have the normal axisorientation. Next in the alternating axis arrangement of the stack 104id the first middle piezoelectric layer. Next in the alternating axisarrangement of the stack 104, is the second middle piezoelectric layer.Next in the alternating axis arrangement of the stack 104 is the toppiezoelectric layer. For the alternating axis arrangement of the stack104, stress 173 excited by the applied oscillating electric field causesnormal axis piezoelectric layers to be in compression, while reverseaxis piezoelectric layers are in extension. Accordingly, FIG. 1B showspeaks of stress 173 on the right side of the heavy dashed line to depictcompression in normal axis piezoelectric layers (e.g., bottom and secondmiddle piezoelectric layers), while peaks of stress 173 are shown on theleft side of the heavy dashed line to depict extension in reverse axispiezoelectric layers (e.g., first middle and top piezoelectric layers).

In operation of the BAW resonator shown in FIG. 1B, peaks of standingwave acoustic energy may correspond to absolute value of peaks of stress173 as shown in FIG. 1B (e.g., peaks of standing wave acoustic energymay correspond to squares of absolute value of peaks of stress 173 asshown in FIG. 1B). In operation of the BAW resonator, standing waveacoustic energy may be coupled through the harmonically tuned top sensorelectrode 115, through isolation layer 167 and into functionalized layer168 of sensing region 116 shown in FIG. 1B.

Standing wave acoustic energy may be coupled into the multilayer metalacoustic reflector electrode 113 shown in FIG. 1B in operation of theBAW resonator. A second member of the first pair of bottom metalelectrode layers may have a relatively high acoustic impedance (e.g.,high acoustic impedance metal layer, e.g., tungsten layer). A firstmember of the first pair of bottom metal electrode layers may have arelatively low acoustic impedance (e.g., low acoustic impedance metallayer, e.g., titanium layer). Accordingly, the first member of the firstpair of bottom metal electrode layers may have acoustic impedance thatis relatively lower than the acoustic impedance of the second member.The first member 119 having the relatively lower acoustic impedance maybe arranged, for example as shown in FIG. 1B, sufficiently proximate toa first layer of piezoelectric material (e.g. sufficiently proximate tobottom layer of piezoelectric material, e.g., sufficiently proximate tostack of piezoelectric material) so that standing wave acoustic energyto be in the first member is greater than respective standing waveacoustic energy to be in other respective layers of the multi-layermetal bottom acoustic reflector electrode 113 in operation of the BAWresonator (e.g. greater than standing wave acoustic energy in the secondmember of the first pair of bottom metal electrode layers, e.g., greaterthan standing wave acoustic energy in the first member of the secondpair of bottom metal electrode layers, e.g., greater than standing waveacoustic energy in the second member of the second pair of bottom metalelectrode layers, e.g., greater than standing wave acoustic energy inthe first member of the third pair of bottom metal electrode layers,e.g., greater than standing wave acoustic energy in the second member ofthe third pair of bottom metal electrode layers, e.g., greater thanstanding wave acoustic energy in the first member of the fourth pair ofbottom metal electrodes, e.g., greater than standing wave acousticenergy in the second member of the fourth pair of bottom metalelectrodes. This may facilitate suppressing parasitic lateral resonancesin operation of the BAW resonator shown in FIG. 1B.

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure 100A corresponding to the cross sectional view ofFIG. 1A, and also shows another simplified top plan view of analternative bulk acoustic wave resonator structure 100B. The bulkacoustic wave resonator structure 100A includes the stack 104A of fourlayers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104A of piezoelectric layers may be sandwichedbetween the multilayer metal acoustic reflector electrode 113A andharmonically tuned top sensor electrode 115A. The multilayer metalacoustic reflector electrode comprise the stack of the plurality ofbottom metal electrode layers of the multilayer metal acoustic reflectorelectrode 113A, e.g., having the alternating arrangement of low acousticimpedance bottom metal electrode layers and high acoustic impedancebottom metal layers. Top electrical interconnect 171A extends over(e.g., electrically contacts) an extremity of harmonically tuned topsensor electrode 115A. Bottom electrical interconnect 169A extends over(e.g., electrically contacts) an extremity of multilayer metal acousticreflector electrode 113A through bottom via region 168A.

FIG. 1C also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure 100B having an apodized shape.The bulk acoustic wave resonator structure 100B includes the stack 104Bof four layers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104B of piezoelectric layers may be sandwichedbetween the multilayer metal acoustic reflector electrode 113B andharmonically tuned top sensor electrode 115B. Harmonically tuned topsensor electrode 115B may have the alternative apodized shape ofalternative bulk acoustic wave resonator structure 100B. The multilayermetal acoustic reflector electrode may comprise the stack of theplurality of bottom metal electrode layers of the multilayer metalacoustic reflector electrode 113B, e.g., having the alternatingarrangement of low acoustic impedance bottom metal electrode layers andhigh acoustic impedance bottom metal layers. Top electrical interconnect171B extends over (e.g., electrically contacts) an extremity ofharmonically tuned top sensor electrode 115B. Bottom electricalinterconnect 169B extends over (e.g., electrically contacts) anextremity of multilayer metal acoustic reflector electrode 113B throughbottom via region 168B.

In FIGS. 1D and 1E, Nitrogen (N) atoms are depicted with a hatchingstyle, while Aluminum (Al) atoms are depicted without a hatching style.FIG. 1D is a perspective view of an illustrative model of a reverse axiscrystal structure 175 of Aluminum Nitride, AlN, in piezoelectricmaterial of layers in FIG. 1A, e.g., having reverse axis orientation ofnegative polarization. For example, first middle and top piezoelectriclayers 107, 111 discussed previously herein with respect to FIGS. 1A and1B are reverse axis piezoelectric layers. By convention, when the firstlayer of normal axis crystal structure 175 is a Nitrogen, N, layer andsecond layer in an upward direction (in the depicted orientation) is anAluminum, Al, layer, the piezoelectric material including the reverseaxis crystal structure 175 is said to have crystallographic c-axisnegative polarization, or reverse axis orientation as indicated by theupward pointing arrow 177. For example, polycrystalline thin filmAluminum Nitride, AlN, may be grown in the crystallographic c-axisnegative polarization, or reverse axis, orientation perpendicularrelative to the substrate surface using reactive magnetron sputtering ofan aluminum target in a nitrogen atmosphere, and by introducing oxygeninto the gas atmosphere of the reaction chamber during fabrication atthe position where the flip to the reverse axis is desired. An inertgas, for example, Argon may also be included in a sputtering gasatmosphere, along with the nitrogen and oxygen.

For example, a predetermined amount of oxygen containing gas may beadded to the gas atmosphere over a short predetermined period of time orfor the entire time the reverse axis layer is being deposited. Theoxygen containing gas may be diatomic oxygen containing gas, such asoxygen (O2). Proportionate amounts of the Nitrogen gas (N2) and theinert gas may flow, while the predetermined amount of oxygen containinggas flows into the gas atmosphere over the predetermined period of time.For example, N2 and Ar gas may flow into the reaction chamber inapproximately a 3:1 ratio of N2 to Ar, as oxygen gas also flows into thereaction chamber. For example, the predetermined amount of oxygencontaining gas added to the gas atmosphere may be in a range from abouta thousandth of a percent (0.001%) to about ten percent (10%), of theentire gas flow. The entire gas flow may be a sum of the gas flows ofargon, nitrogen and oxygen, and the predetermined period of time duringwhich the predetermined amount of oxygen containing gas is added to thegas atmosphere may be in a range from about a quarter (0.25) second to alength of time needed to create an entire layer, for example. Forexample, based on mass-flows, the oxygen composition of the gasatmosphere may be about 2 percent when the oxygen is briefly injected.This results in an aluminum oxynitride (ALON) portion of the finalmonolithic piezoelectric layer, integrated in the Aluminum Nitride, AlN,material, having a thickness in a range of about 5 nm to about 20 nm,which is relatively oxygen rich and very thin. Alternatively, the entirereverse axis piezoelectric layer may be aluminum oxynitride.

FIG. 1E is a perspective view of an illustrative model of a normal axiscrystal structure 179 of Aluminum Nitride, AlN, in piezoelectricmaterial of layers in FIG. 1A, e.g., having normal axis orientation ofpositive polarization. For example, bottom and second middlepiezoelectric layers 105, 109 discussed previously herein with respectto FIGS. 1A and 1B are normal axis piezoelectric layers. By convention,when the first layer of the reverse axis crystal structure 179 is an Allayer and second layer in an upward direction (in the depictedorientation) is an N layer, the piezoelectric material including thereverse axis crystal structure 179 is said to have a c-axis positivepolarization, or normal axis orientation as indicated by the downwardpointing arrow 181. For example, polycrystalline thin film MN may begrown in the crystallographic c-axis positive polarization, or normalaxis, orientation perpendicular relative to the substrate surface byusing reactive magnetron sputtering of an Aluminum target in a nitrogenatmosphere.

FIGS. 2A through 2E show further simplified views of bulk acoustic waveresonators similar to the bulk acoustic wave resonator structure shownin FIG. 1A. In addition to further simplified views of bulk acousticwave resonators, FIGS. 2A and 2B show corresponding impedance versusfrequency response during its electrical operation, as well asalternative bulk acoustic wave resonator structures with differingnumbers of alternating axis piezoelectric layers, and their respectivecorresponding impedance versus frequency response during electricaloperation. FIG. 2C shows additional alternative bulk acoustic waveresonator structures with additional numbers of alternating axispiezoelectric layers. FIGS. 2D and 2E show more additional alternativebulk acoustic wave resonator structures. Bulk acoustic wave resonators2001A through 2001K may, but need not be, bulk acoustic millimeter waveresonators 2001A through 2001K, operable with a main resonance modehaving a main resonant frequency that is a millimeter wave frequency(e.g., twenty-four Gigahertz, 24 GHz) in a millimeter wave frequencyband. As defined herein, millimeter wave means a wave having a frequencywithin a range extending from eight Gigahertz (8 GHz) to three hundredGigahertz (300 GHz), and millimeter wave band means a frequency bandspanning this millimeter wave frequency range from eight Gigahertz (8GHz) to three hundred Gigahertz (300 GHz). Bulk acoustic wave resonators2001A through 2001K may, but need not be, bulk acoustic Super HighFrequency (SHF) wave resonators 2001A through 2001K or bulk acousticExtremely High Frequency (EHF) wave resonators 2001A through 2001K, asthe terms Super High Frequency (SHF) and Extremely High Frequency (EHF)are defined by the International Telecommunications Union (ITU). Forexample, bulk acoustic wave resonators 2001A through 2001K may be bulkacoustic Super High Frequency (SHF) wave resonators 2001A through 2001Koperable with a main resonance mode having a main resonant frequencythat is a Super High Frequency (SHF) (e.g., twenty-four Gigahertz, 24GHz) in a Super High Frequency (SHF) wave frequency band. Piezoelectriclayer thicknesses may be selected to determine the main resonantfrequency of bulk acoustic Super High Frequency (SHF) wave resonators2001A through 2001K in the Super High Frequency (SHF) wave band (e.g.,twenty-four Gigahertz, 24 GHz main resonant frequency).

Similarly, layer thicknesses of Super High Frequency (SHF) reflectorlayers (e.g., layer thickness of multilayer metal acoustic SHF reflectorelectrodes 1013A through 2013K) may be selected to determine quarterwavelength resonant frequency of such SHF reflectors at a frequency,e.g., quarter wavelength resonant frequency, within the Super HighFrequency (SHF) wave band. For example, layer thickness of de-tunedmulti-layer metal acoustic SHF wave reflector bottom electrodes 2013Athrough 2013K may be acoustically de-tuned (e.g., tuned down infrequency) from the resonant frequency (e.g. main resonant frequency) ofthe BAW resonator (e.g., tuned down to have a quarter wavelengthresonant frequency that is lower than the 24 GHz main resonant frequencyof the SHF BAW resonator). Similarly, layer thicknesses of Super HighFrequency (SHF) harmonically tuned top sensor electrodes (e.g., layerthickness of SHF harmonically tuned top sensor electrodes 2015A through2015K) may be selected to determine half wavelength resonant frequencyof such SHF harmonically tuned top sensor electrodes at a frequency,e.g., half wavelength resonant frequency, within the Super HighFrequency (SHF) wave band. For example, layer thickness of de-tuned ofSHF harmonically tuned top sensor electrodes 2015A through 2015K may beacoustically de-tuned (e.g., tuned up in frequency) from the resonantfrequency (e.g. main resonant frequency) of the BAW resonator (e.g.,tuned up to have a half wavelength resonant frequency that is higherthan a 24 GHz main resonant frequency of the SHF BAW resonator, e.g.,tuned up to have a half wavelength resonant frequency that is higherthan the 24 GHz main resonant frequency of the SHF BAW resonator).

Alternatively, bulk acoustic wave resonators 2001A through 2001K may bebulk acoustic Extremely High Frequency (EHF) wave resonators 2001Athrough 2001K operable with a main resonance mode having a main resonantfrequency that is an Extremely High Frequency (EHF) wave band (e.g.,thirty-nine Gigahertz, 39 GHz main resonant frequency, e.g.,seventy-seven Gigahertz, 77 GHz main resonant frequency) in an ExtremelyHigh Frequency (EHF) wave frequency band. As discussed previouslyherein, piezoelectric layer thicknesses may be selected to determine themain resonant frequency of bulk acoustic Extremely High Frequency (EHF)wave resonators 2001A through 2001K in the Extremely High Frequency(EHF) wave band (e.g., thirty-nine Gigahertz, 39 GHz main resonantfrequency, e.g., seventy-seven Gigahertz, 77 GHz main resonantfrequency). Similarly, layer thicknesses of Extremely High Frequency(EHF) reflector layers (e.g., layer thickness of multilayer metalacoustic EHF reflector electrodes 1013A through 2013K) may be selectedto determine quarter wavelength resonant frequency of such EHFreflectors at a frequency, e.g., quarter wavelength resonant frequency,within the Extremely High Frequency (EHF) wave band. For example, layerthickness of de-tuned multi-layer metal acoustic EHF wave reflectorbottom electrodes 2013A through 2013K may be acoustically de-tuned(e.g., tuned down in frequency) from the resonant frequency (e.g. mainresonant frequency) of the BAW resonator (e.g., tuned down to have aquarter wavelength resonant frequency that is lower than a 77 GHz mainresonant frequency of the EHF BAW resonator, e.g., tuned down to have aquarter wavelength resonant frequency that is lower than the 77 GHz mainresonant frequency of the EHF BAW resonator). Similarly, layerthicknesses of Super High Frequency (SHF) harmonically tuned top sensorelectrodes (e.g., layer thickness of EHF harmonically tuned top sensorelectrodes 2015A through 2015K) may be selected to determine halfwavelength resonant frequency of such EHF harmonically tuned top sensorelectrodes at a frequency, e.g., half wavelength resonant frequency,within the Super High Frequency (SHF) wave band. For example, layerthickness of de-tuned of EHF harmonically tuned top sensor electrodes2015A through 2015K may be acoustically de-tuned (e.g., tuned up infrequency) from the resonant frequency (e.g. main resonant frequency) ofthe BAW resonator (e.g., tuned up to have a half wavelength resonantfrequency that is up higher than the 77 GHz main resonant frequency ofthe EHF BAW resonator).

The general structures of the harmonically tuned top sensor electrodeand the multilayer metal acoustic reflector electrode have already beendiscussed previously herein with respect of FIGS. 1A and 1B. As alreadydiscussed, the multilayer metal acoustic reflector electrode is directedto respective pairs of metal electrode layers, in which a first memberof the pair has a relatively low acoustic impedance (relative toacoustic impedance of another member of the pair), in which the othermember of the pair has a relatively high acoustic impedance (relative toacoustic impedance of the first member of the pair).

For example, in bottom de-tuned reflector electrodes 2013A through 2013Iand 2013K, the first member having the relatively lower acousticimpedance of the first pair may be arranged nearest, e.g. may abut, afirst piezoelectric layer (e.g. bottom piezoelectric layer of the BAWresonator, e.g., piezoelectric stack of the BAW resonator). For example,in bottom de-tuned reflector electrodes 2013J, the first member of thefirst pair of layers of bottom de-tuned reflector electrodes 2013Jhaving the relatively lower acoustic impedance of the first pair may bearranged substantially nearest, e.g. may substantially abut, the firstpiezoelectric layer (e.g. bottom piezoelectric layer of the BAWresonator, e.g., piezoelectric stack of the BAW resonator). This mayfacilitate suppressing parasitic lateral modes. In bottom de-tunedreflector electrodes 2013A through 2013K, the first member having therelatively lower acoustic impedance may be arranged sufficientlyproximate to the first layer of piezoelectric material (e.g. may bearranged sufficiently proximate to the bottom piezoelectric layer, e.g.may be arranged sufficiently proximate to the piezoelectric stack), sothat the first member having the relatively lower acoustic impedance maycontribute more to the multilayer metal acoustic reflector electrodebeing acoustically de-tuned from the resonant frequency of the BAWresonator than is contributed by any other bottom metal electrode layerof the multilayer metal acoustic reflector electrode. In bottom de-tunedreflector electrodes 2013A through 2013K, the first member having therelatively lower acoustic impedance may be arranged sufficientlyproximate to the first layer of piezoelectric material (e.g. may bearranged sufficiently proximate to the bottom piezoelectric layer, e.g.may be arranged sufficiently proximate to the piezoelectric stack), sothat the first member having the relatively lower acoustic impedance maycontribute more, e.g., may contribute more to facilitate suppressingparasitic lateral resonances in operation of the BAW resonator than iscontributed by any other bottom metal electrode layer of the multilayermetal acoustic reflector electrode.

Shown in FIG. 2A is a bulk acoustic SHF or EHF wave resonator 2001Aincluding a normal axis piezoelectric layer 201A sandwiched between SHFor EHF detuned harmonically tuned top sensor electrode 2015A andmulti-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013A. For the single piezoelectric layer 201A of bulkacoustic SHF or EHF wave resonator 2001A, simulation may predict optimalfacilitation of suppressing parasitic lateral resonances by de-tuning ofthe resonant frequency of the bulk acoustic wave resonator 2001A, forde-tuning of SHF or EHF harmonically tuned top sensor electrode 2015Aand the multi-layer metal bottom de-tuned acoustic SHF or EHF wavereflector electrode 2013A. Also shown in FIG. 2A is a bulk acoustic SHFor EHF wave resonator 2001B including a normal axis piezoelectric layer201B and a reverse axis piezoelectric layer 202B arranged in a twopiezoelectric layer alternating stack arrangement sandwiched between SHFor EHF detuned harmonically tuned top sensor electrode 2015B and detunedmulti-layer metal acoustic SHF or EHF wave reflector bottom electrode2013B. For the two piezoelectric layer 201B, 202B of bulk acoustic SHFor EHF wave resonator 2001B, simulation may predict optimal facilitationof suppressing parasitic lateral resonances by de-tuning of the resonantfrequency of the bulk acoustic wave resonator 2001B, for de-tuning ofthe SHF or EHF detuned harmonically tuned top sensor electrode 2015B andthe multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013B. A bulk acoustic SHF or EHF wave resonator 2001Cincludes a normal axis piezoelectric layer 201C, a reverse axispiezoelectric layer 202C, and another normal axis piezoelectric layer203C arranged in a three piezoelectric layer alternating stackarrangement sandwiched between SHF or EHF detuned harmonically tuned topsensor electrode 2015C and detuned multi-layer metal acoustic SHF or EHFwave reflector bottom electrode 2013C. For the three piezoelectric layer201C, 202C, 203C of bulk acoustic SHF or EHF wave resonator 2001C,simulation may predict optimal facilitation of suppressing parasiticlateral resonances by de-tuning of the resonant frequency of the bulkacoustic wave resonator 2001C, for de-tuning of the SHF or EHF detunedharmonically tuned top sensor electrode 2015C and de-tuning of themulti-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013C.

Included in FIG. 2B is bulk acoustic SHF or EHF wave resonator 2001D ina further simplified view similar to the bulk acoustic wave resonatorstructure shown in FIGS. 1A and 1B and including a normal axispiezoelectric layer 201D, a reverse axis piezoelectric layer 202D, andanother normal axis piezoelectric layer 203D, and another reverse axispiezoelectric layer 204D arranged in a four piezoelectric layeralternating stack arrangement sandwiched between SHF or EHF detunedharmonically tuned top sensor electrode 2015D and multi-layer metalacoustic SHF or EHF wave reflector bottom electrode 2013D. For the fourpiezoelectric layer 201D, 202D, 203D, 204D of bulk acoustic SHF or EHFwave resonator 2001D, simulation may predict optimal facilitation ofsuppressing parasitic lateral resonances by de-tuning of the resonantfrequency of the bulk acoustic wave resonator 2001D, for de-tuning ofthe SHF or EHF detuned harmonically tuned top sensor electrode 2015D andthe multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013D. A bulk acoustic SHF or EHF wave resonator 2001Eincludes a normal axis piezoelectric layer 201E, a reverse axispiezoelectric layer 202E, another normal axis piezoelectric layer 203E,another reverse axis piezoelectric layer 204E, and yet another normalaxis piezoelectric layer 205E arranged in a five piezoelectric layeralternating stack arrangement sandwiched between SHF or EHF detunedharmonically tuned top sensor electrode 2015E and multi-layer metalacoustic SHF or EHF wave reflector bottom electrode 2013E. For the fivepiezoelectric layer 201E, 202E, 203E, 204E, 205E of bulk acoustic SHF orEHF wave resonator 2001E, simulation may predict optimal facilitation ofsuppressing parasitic lateral resonances by de-tuning of the resonantfrequency of the bulk acoustic wave resonator 2001E, for de-tuning ofthe SHF or EHF detuned harmonically tuned top sensor electrode 2015E andthe multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013E. A bulk acoustic SHF or EHF wave resonator 2001Fincludes a normal axis piezoelectric layer 201F, a reverse axispiezoelectric layer 202F, another normal axis piezoelectric layer 203F,another reverse axis piezoelectric layer 204F, yet another normal axispiezoelectric layer 205F, and yet another reverse axis piezoelectriclayer 206F arranged in a six piezoelectric layer alternating stackarrangement sandwiched between SHF or EHF detuned harmonically tuned topsensor electrode 2015F and multi-layer metal acoustic SHF or EHF wavereflector bottom electrode 2013F. For the six piezoelectric layer 201F,202F, 203F, 204F, 205F, 206F of bulk acoustic SHF or EHF wave resonator2001F, simulation may predict optimal facilitation of suppressingparasitic lateral resonances by de-tuning of the resonant frequency ofthe bulk acoustic wave resonator 2001F, for de-tuning of the SHF or EHFdetuned harmonically tuned top sensor electrode 2015F and themulti-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013F.

In FIG. 2A, shown directly to the right of the bulk acoustic SHF or EHFwave resonator 2001A including the normal axis piezoelectric layer 201Aand half-wavelength thick harmonically tuned top sensing electrode2015A, is a corresponding diagram 2019A depicting its impedance versusfrequency response during its electrical operation, as predicted bysimulation. The diagram 2019A depicts the main resonant peak 2021A ofthe main resonant mode (e.g., main series resonant peak 2021A) of thebulk acoustic SHF or EHF wave resonator 2001A at its main resonantfrequency (e.g., its 24 GHz series resonant frequency, e.g., its mainseries resonant frequency, e.g., Fs) and main parallel resonant peak2022A of the bulk acoustic SHF or EHF wave resonator 2001A at its mainparallel resonant frequency, Fp. The diagram 2019A also depicts thesatellite resonance peaks 2023A, 2025A of the satellite resonant modesof the bulk acoustic SHF or EHF wave resonator 2001A at satellitefrequencies above and below the main resonant frequency 2021A (e.g.,above and below the 24 GHz series resonant frequency). Relativelyspeaking, the main resonant mode corresponding to the main resonancepeak 2021A is the strongest resonant mode because it is stronger thanother resonant modes of the resonator 2001A, (e.g., stronger than thesatellite modes corresponding to relatively lesser satellite resonancepeaks 2023A, 2025A).

Similarly, in FIGS. 2A and 2B, shown directly to the right of the bulkacoustic SHF or EHF wave resonators 2001B through 2001F are respectivecorresponding diagrams 2019B through 2019F depicting correspondingimpedance versus frequency response during electrical operation, aspredicted by simulation. The resonators 2001B, 2001D and 2001F compriseone wavelength thick harmonically tuned top sensing electrodes 2015B,2015D and 2015F, respectively, while the resonators 2001C and 2001Ecomprise half-wavelength thick harmonically tuned top sensing electrodes2015C and 2015E, respectively. The diagrams 2019B through 2019F depictrespective example SHF main resonant peaks 2021B through 2021F ofrespective corresponding main resonant modes of bulk acoustic SHF waveresonators 2001B through 2001F at respective corresponding main resonantfrequencies (e.g., respective 24 GHz series resonant frequencies, e.g.,main series resonant frequencies, Fs) and main parallel resonant peak2022B through 2022F of the bulk acoustic SHF or EHF wave resonator 2001Aat its main parallel resonant frequencies, Fp. The diagrams 2019Bthrough 2019F also depict respective example SHF satellite resonancepeaks 2023B through 2023F, 2025B through 2025F of respectivecorresponding satellite resonant modes of the bulk acoustic SHF waveresonators 2001B through 2001F at respective corresponding SHF satellitefrequencies above and below the respective corresponding main SHFresonant frequencies 2021B through 2021F (e.g., above and below thecorresponding respective 24 GHz series resonant frequencies). Relativelyspeaking, for the corresponding respective main SHF resonant modes, itscorresponding respective SHF main resonance peak 2021B through 2021F isthe strongest for its bulk acoustic SHF wave resonators 2001B through2001F (e.g., stronger than the corresponding respective SHF satellitemodes and corresponding respective lesser SHF satellite resonance peaks2023B, 2025B).

As mentioned previously, FIG. 2C shows additional alternative bulkacoustic wave resonator structures with additional numbers ofalternating axis piezoelectric layers. A bulk acoustic SHF or EHF waveresonator 2001G includes four normal axis piezoelectric layers 201G,203G, 205G, 207G, and four reverse axis piezoelectric layers 202G, 204G,206G, 208G arranged in an eight piezoelectric layer alternating stackarrangement sandwiched between SHF or EHF detuned harmonically tuned topsensor electrode 2015G and multi-layer metal bottom de-tuned acousticSHF or EHF wave reflector electrode 2013G. For the eight piezoelectriclayer 201G, 202G, 203G, 204G, 205G, 206G, 207G, 208G of bulk acousticSHF or EHF wave resonator 2001G, simulation may predict optimalfacilitation of suppressing parasitic lateral resonances by de-tuning ofthe resonant frequency of the bulk acoustic wave resonator 2001G, forde-tuning of the SHF or EHF detuned harmonically tuned top sensorelectrode 2015G and the multi-layer metal bottom de-tuned acoustic SHFor EHF wave reflector electrode 2013G. A bulk acoustic SHF or EHF waveresonator 2001H includes five normal axis piezoelectric layers 201H,203H, 205H, 207H, 209H and five reverse axis piezoelectric layers 202H,204H, 206H, 208H, 210H arranged in a ten piezoelectric layer alternatingstack arrangement sandwiched between SHF or EHF detuned harmonicallytuned top sensor electrode 2015H and multi-layer metal bottom acousticSHF or EHF wave reflector electrode 2013H. For the ten piezoelectriclayer 201H, 202H, 203H, 204H, 205H, 206H, 207H, 208H, 209H, 210H of bulkacoustic SHF or EHF wave resonator 2001H, simulation may predict optimalfacilitation of suppressing parasitic lateral resonances by de-tuning ofthe resonant frequency of the bulk acoustic wave resonator 2001H, forde-tuning of the SHF or EHF detuned harmonically tuned top sensorelectrode 2015H and the multi-layer metal bottom de-tuned acoustic SHFor EHF wave reflector electrode 2013H. A bulk acoustic SHF or EHF waveresonator 2001I includes nine normal axis piezoelectric layers 201I,203I, 205I, 207I, 209I, 211I, 213I, 215I, 217I and nine reverse axispiezoelectric layers 202I, 204I, 206I, 208I, 210I, 212I, 214I, 216I,218I arranged in an eighteen piezoelectric layer alternating stackarrangement sandwiched between SHF or EHF detuned harmonically tuned topsensor electrode 2015I and multi-layer metal bottom de-tuned acousticSHF or EHF wave reflector bottom electrode 2013I. For the eighteenpiezoelectric layer 201I, 202I, 203I, 204I, 205I, 206I, 207I, 208I,209I, 210I, 211I, 212I, 213I, 214I, 215I, 216I, 217I, 218I of bulkacoustic SHF or EHF wave resonator 2001H, simulation may predict optimalfacilitation of suppressing parasitic lateral resonances by de-tuning ofthe resonant frequency of the bulk acoustic wave resonator 2001I, forde-tuning of the SHF or EHF detuned harmonically tuned top sensorelectrode 2015I and the multi-layer metal bottom de-tuned acoustic SHFor EHF wave reflector electrode 2013I.

In the example resonators, 2001A through 2001F, of FIGS. 2A through 2B,respective sensing region 216A through 216F is explicitly shown. For thesake of simplicity in the example resonators 2001G through 2001I of FIG.2C, respective sensing regions are present but are not explicitly shown.In the example resonators, 2001A through 2001I, of FIGS. 2A through 2C,a notional heavy dashed line is used in depicting respective etched edgeregion, 253A through 253I, associated with the example resonators, 2001Athrough 2001I. Similarly, in the example resonators, 2001A through2001I, of FIGS. 2A through 2C, a laterally opposed etched edge region254A through 254I may be arranged laterally opposite from etched edgeregion, 253A through 253I. The respective etched edge region may, butneed not, assist with acoustic isolation of the resonators, 2001Athrough 2001I. The respective etched edge region may, but need not, helpwith avoiding acoustic losses for the resonators, 2001A through 2001I.The respective etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend along thethickness dimension of the respective piezoelectric layer stack. Therespective etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend through (e.g.,entirely through or partially through) the respective piezoelectriclayer stack. The respective etched edge region, 253A through 253I mayextend through (e.g., entirely through or partially through) therespective first piezoelectric layer, 201A through 201I. The respectiveetched edge region, 253B through 253I, (and the laterally opposed etchededge region 254B through 254I) may extend through (e.g., entirelythrough or partially through) the respective second piezoelectric layer,202B through 202I. The respective etched edge region, 253C through 253I,(and the laterally opposed etched edge region 254C through 254I) mayextend through (e.g., entirely through or partially through) therespective third piezoelectric layer, 203C through 203I. The respectiveetched edge region, 253D through 253I, (and the laterally opposed etchededge region 254D through 254I) may extend through (e.g., entirelythrough or partially through) the respective fourth piezoelectric layer,204D through 204I. The respective etched edge region, 253E through 253I,(and the laterally opposed etched edge region 254E through 254I) mayextend through (e.g., entirely through or partially through) therespective additional piezoelectric layers of the resonators, 2001Ethrough 2001I. The respective etched edge region, 253A through 253I,(and the laterally opposed etched edge region 254A through 254I) mayextend along the thickness dimension of the respective multi-layer metalacoustic SHF or EHF wave reflector bottom electrode, 2013A through2013I, of the resonators, 2001A through 2001I. The respective etchededge region, 253A through 253I, (and the laterally opposed etched edgeregion 254A through 254I) may extend through (e.g., entirely through orpartially through) the respective, 2013A through 2013I. The respectiveetched edge region, 253A through 253I, (and the laterally opposed etchededge region 254A through 254I) may extend along the thickness dimensionof the respective SHF or EHF detuned harmonically tuned top sensorelectrode 2015A through 2015I of the resonators, 2001A through 2001I.The etched edge region, 253A through 253I, (and the laterally opposedetched edge region 254A through 254I) may extend through (e.g., entirelythrough or partially through) the respective multi-layer metal bottomde-tuned acoustic SHF or EHF wave reflector electrode, 2013A through2013I.

As shown in FIGS. 2A through 2C, first mesa structures corresponding tothe respective stacks of piezoelectric material layers may extendlaterally between (e.g., may be formed between) etched edge regions 253Athrough 253I and laterally opposing etched edge region 254A through254I. Second mesa structures corresponding to multi-layer metal bottomde-tuned acoustic SHF or EHF wave reflector electrode 2013A through2013I may extend laterally between (e.g., may be formed between) etchededge regions 253A through 253I and laterally opposing etched edge region254A through 254I. Third mesa structures corresponding to SHF or EHFdetuned harmonically tuned top sensor electrode 2015A through 2015I mayextend laterally between (e.g., may be formed between) etched edgeregions 253A through 253I and laterally opposing etched edge region 254Athrough 254I.

In accordance with the teachings herein, various bulk acoustic SHF orEHF wave resonators may include: a seven piezoelectric layer alternatingaxis stack arrangement; a nine piezoelectric layer alternating axisstack arrangement; an eleven piezoelectric layer alternating axis stackarrangement; a twelve piezoelectric layer alternating axis stackarrangement; a thirteen piezoelectric layer alternating axis stackarrangement; a fourteen piezoelectric layer alternating axis stackarrangement; a fifteen piezoelectric layer alternating axis stackarrangement; a sixteen piezoelectric layer alternating axis stackarrangement; and a seventeen piezoelectric layer alternating axis stackarrangement; and that these stack arrangements may be sandwiched betweenrespective SHF or EHF detuned harmonically tuned top sensor electrodesand respective multi-layer metal bottom de-tuned acoustic SHF or EHFwave reflector electrodes. As mentioned previously, in accordance withthe teachings of this disclosure, number of member piezoelectric layersin an alternating piezoelectric axis arrangement may be increased indesigns extending to higher resonant frequencies. This may, but need notboost quality factor (Q factor). A total quality factor of the BAWresonator including the sheet resistance of the top electrode may bewithin a range from approximately three hundred to approximately fifteenhundred.

Further, it should be understood that interposer layers as discussedpreviously herein with respect to FIG. 1A are explicitly shown in thesimplified diagrams of the various resonators shown in FIGS. 2A, 2B and2C. Such interposers may be included and interposed between adjacentpiezoelectric layers in the various resonators shown in FIGS. 2A, 2B and2C, and further may be included and interposed between adjacentpiezoelectric layers in the various resonators having the alternatingaxis stack arrangements of various numbers of piezoelectric layers, asdescribed in this disclosure. In some other alternative bulk acousticwave resonator structures, fewer interposer layers may be employed. Forexample, FIG. 2D shows another alternative bulk acoustic wave resonatorstructure 2001J, similar to bulk acoustic wave resonator structure 2001Ishown in FIG. 2C, but with differences. For example, relatively fewerinterposer layers may be included in the alternative bulk acoustic waveresonator structure 2001J shown in FIG. 2D. For example, FIG. 2D shows afirst interposer layer 261J interposed between second layer of (reverseaxis) piezoelectric material 202J and third layer of (normal axis)piezoelectric material 203J, but without an interposer layer interposedbetween first layer of (normal axis) piezoelectric material 201J andsecond layer of (reverse axis) piezoelectric material 202J. As shown inFIG. 2D in a first detailed view 220J, without an interposer layerinterposed between first layer of piezoelectric material 201J and secondlayer of piezoelectric material 202J, the first and second piezoelectriclayer 201J, 202J may be a monolithic layer 222J of piezoelectricmaterial (e.g., Aluminum Nitride (AlN)) having first and second regions224J, 226J. A central region of monolithic layer 222J of piezoelectricmaterial (e.g., Aluminum Nitride (AlN)) between first and second regions224J, 226J may be oxygen rich. The first region 224J of monolithic layer222J (e.g., bottom region 224J of monolithic layer 222J) has a firstpiezoelectric axis orientation (e.g., normal axis orientation) asrepresentatively illustrated in detailed view 220J using a downwardpointing arrow at first region 224J, (e.g., bottom region 224J). Thisfirst piezoelectric axis orientation (e.g., normal axis orientation,e.g., downward pointing arrow) at first region 224J of monolithic layer222J (e.g., bottom region 224J of monolithic layer 222J) corresponds tothe first piezoelectric axis orientation (e.g., normal axis orientation,e.g., downward pointing arrow) of first piezoelectric layer 201J. Thesecond region 226J of monolithic layer 222J (e.g., top region 226J ofmonolithic layer 222J) has a second piezoelectric axis orientation(e.g., reverse axis orientation) as representatively illustrated indetailed view 220J using an upward pointing arrow at second region 226J,(e.g., top region 226J). This second piezoelectric axis orientation(e.g., reverse axis orientation, e.g., upward pointing arrow) at secondregion 226J of monolithic layer 222J (e.g., top region 226J ofmonolithic layer 222J) may be formed to oppose the first piezoelectricaxis orientation (e.g., normal axis orientation, e.g., downward pointingarrow) at first region 224J of monolithic layer 222J (e.g., bottomregion 224J of monolithic layer 222J) by adding gas (e.g., oxygen) toflip the axis while sputtering the second region 226J of monolithiclayer 222J (e.g., top region 226J of monolithic layer 222J) onto thefirst region 224J of monolithic layer 222J (e.g., bottom region 224J ofmonolithic layer 222J). The second piezoelectric axis orientation (e.g.,reverse axis orientation, e.g., upward pointing arrow) at second region226J of monolithic layer 222J (e.g., top region 226J of monolithic layer222J) corresponds to the second piezoelectric axis orientation (e.g.,reverse axis orientation, e.g., upward pointing arrow) of secondpiezoelectric layer 202J.

Similarly, as shown in FIG. 2D in a second detailed view 230J, withoutan interposer layer interposed between third layer of piezoelectricmaterial 203J and fourth layer of piezoelectric material 204J, the thirdand fourth piezoelectric layer 203J, 204J may be an additionalmonolithic layer 232J of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions 234J, 236J. A central region ofadditional monolithic layer 232J of piezoelectric material (e.g.,Aluminum Nitride (AlN)) between first and second regions 234J, 236J maybe oxygen rich. The first region 234J of additional monolithic layer232J (e.g., bottom region 234J of additional monolithic layer 232J) hasthe first piezoelectric axis orientation (e.g., normal axis orientation)as representatively illustrated in second detailed view 230J using thedownward pointing arrow at first region 234J, (e.g., bottom region224J). This first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 234J ofadditional monolithic layer 232J (e.g., bottom region 234J of additionalmonolithic layer 232J) corresponds to the first piezoelectric axisorientation (e.g., normal axis orientation, e.g., downward pointingarrow) of third piezoelectric layer 203J. The second region 236J ofadditional monolithic layer 232J (e.g., top region 236J of additionalmonolithic layer 232J) has the second piezoelectric axis orientation(e.g., reverse axis orientation) as representatively illustrated insecond detailed view 230J using the upward pointing arrow at secondregion 236J, (e.g., top region 236J). This second piezoelectric axisorientation (e.g., reverse axis orientation, e.g., upward pointingarrow) at second region 236J of additional monolithic layer 232J (e.g.,top region 236J of additional monolithic layer 232J) may be formed tooppose the first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 234J ofadditional monolithic layer 232J (e.g., bottom region 234J of additionalmonolithic layer 232J) by adding gas (e.g., oxygen) to flip the axiswhile sputtering the second region 236J of additional monolithic layer232J (e.g., top region 236J of additional monolithic layer 232J) ontothe first region 234J of additional monolithic layer 232J (e.g., bottomregion 234J of additional monolithic layer 232J). The secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at second region 236J of additional monolithiclayer 232J (e.g., top region 236J of additional monolithic layer 232J)corresponds to the second piezoelectric axis orientation (e.g., reverseaxis orientation, e.g., upward pointing arrow) of fourth piezoelectriclayer 204J.

Similar to what was just discussed, without an interposer layerinterposed between fifth layer of piezoelectric material 205J and sixthlayer of piezoelectric material 206J, the fifth and sixth piezoelectriclayer 205J, 206J may be another additional monolithic layer ofpiezoelectric material (e.g., Aluminum Nitride (AlN)) having first andsecond regions. More generally, for example in FIG. 2D, where N is anodd positive integer, without an interposer layer interposed between Nthlayer of piezoelectric material and (N+1)th layer of piezoelectricmaterial, the Nth and (N+1)th piezoelectric layer may be an (N+1)/2thmonolithic layer of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions. Accordingly, without aninterposer layer interposed between seventeenth layer of piezoelectricmaterial 217J and eighteenth layer of piezoelectric material 218J, theseventeenth and eighteenth piezoelectric layer 217J, 218J may be ninthmonolithic layer of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions.

The first interposer layer 261J is shown in FIG. 2D as interposingbetween a first pair of opposing axis piezoelectric layers 201J, 202J,and a second pair of opposing axis piezoelectric layers 203J, 204J. Moregenerally, for example, where M is a positive integer, an Mth interposerlayer is shown in FIG. 2D as interposing between an Mth pair of opposingaxis piezoelectric layers and an (M+1)th pair of opposing axispiezoelectric layers. Accordingly, an eighth interposer layer is shownin FIG. 2D as interposing between an eighth pair of opposing axispiezoelectric layers 215J, 216J, and a ninth pair of opposing axispiezoelectric layers 217J, 218J. FIG. 2D shows an eighteen piezoelectriclayer alternating axis stack arrangement sandwiched between SHF or EHFdetuned harmonically tuned top sensor electrodes 2015J and multi-layermetal bottom de-tuned acoustic SHF or EHF wave reflector electrode2013J. Etched edge region 253J (and laterally opposing etched edgeregion 254J) may extend through (e.g., entirely through, e.g., partiallythrough) the eighteen piezoelectric layer alternating axis stackarrangement and its interposer layers, and may extend through (e.g.,entirely through, e.g., partially through) SHF or EHF detunedharmonically tuned top sensor electrodes 2015J, and may extend through(e.g., entirely through, e.g., partially through) multi-layer metalbottom de-tuned acoustic SHF or EHF wave reflector electrode 2013J. Asshown in FIG. 2D, a first mesa structure corresponding to the stack ofeighteen piezoelectric material layers may extend laterally between(e.g., may be formed between) etched edge region 253J and laterallyopposing etched edge region 254J. A second mesa structure correspondingto multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013J may extend laterally between (e.g., may be formedbetween) etched edge region 253J and laterally opposing etched edgeregion 254J. Third mesa structure corresponding to SHF or EHF detunedharmonically tuned top sensor electrodes 2015J may extend laterallybetween (e.g., may be formed between) etched edge region 253J andlaterally opposing etched edge region 254J.

As mentioned previously herein, one or more (e.g., one or a pluralityof) interposer layers may be metal interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be dielectric interposer layers. Interposer layers may bemetal and/or dielectric interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different metal layers. For example, highacoustic impedance metal layer such as Tungsten (W), Molybdenum (Mo) may(but need not) raise effective electromechanical coupling coefficient(Kt2) while subsequently deposited metal layer with hexagonal symmetrysuch as Titanium (Ti) may (but need not) facilitate highercrystallographic quality of subsequently deposited piezoelectric layer.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be formed of different dielectric layers. Forexample, high acoustic impedance dielectric layer such as HafniumDioxide (HfO2) may (but need not) raise effective electromechanicalcoupling coefficient (Kt2). Subsequently deposited amorphous dielectriclayer such as Silicon Dioxide (SiO2) may (but need not) facilitatecompensating for temperature dependent frequency shifts. Alternativelyor additionally, one or more (e.g., one or a plurality of) interposerlayers may comprise metal and dielectric for respective interposerlayers. For example, high acoustic impedance metal layer such asTungsten (W), Molybdenum (Mo) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2) while subsequentlydeposited amorphous dielectric layer such as Silicon Dioxide (SiO2) may(but need not) facilitate compensating for temperature dependentfrequency shifts. For example, in FIG. 2D one or more of the interposerlayers (e.g., interposer layer 268J) may comprise metal and dielectricfor respective interposer layers. For example, detailed view 240J ofinterposer 268J shows interposer 268J as comprising metal sub-layer268JB over dielectric sub-layer 268JA. For interposer 268J, examplethickness of metal sub-layer 268JB may be approximately two hundredAngstroms (200 A). For interposer 268J, example thickness of dielectricsub-layer 268JA may be approximately two hundred Angstroms (200 A). Thesecond piezoelectric axis orientation (e.g., reverse axis orientation,e.g., upward pointing arrow) at region 244J (e.g., bottom region 244J)corresponds to the second piezoelectric axis orientation (e.g., reverseaxis orientation, e.g., upward pointing arrow) of eighth piezoelectriclayer 208J. The first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at region 246J (e.g., topregion 246J) corresponds to the first piezoelectric axis orientation(e.g., normal orientation, e.g., downward pointing arrow) of ninthpiezoelectric layer 209J.

FIG. 2D shows sensing region 216J acoustically coupled with SHF or EHFdetuned harmonically tuned top sensor electrode 2015. Multi-layer metalbottom de-tuned acoustic SHF or EHF wave reflector electrode 2013J maycomprise a first pair of metal top electrode layers (not shown).Multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 2013J may also include additional similar pairs (not shown) ofalternating high acoustic impedance metal layers. The first pair ofmetal top electrode layers may comprise a first member of low acousticimpedance metal layer and a second member of high acoustic impedancemetal layer (not shown). In addition to the first pair of metal bottomelectrode layers (not shown), the multi-layer metal bottom de-tunedacoustic SHF or EHF wave reflector electrode may include additionalpairs (not shown) of alternating high acoustic impedance/low acousticmetal layers. In multi-layer metal bottom de-tuned acoustic SHF or EHFwave reflector electrode 2013J, the first member of low acousticimpedance metal layer (not shown) may be arranged nearer to apiezoelectric layer (e.g., nearer to bottom piezoelectric layer 201J,e.g., nearer to stack of piezoelectric layers 254J) than second memberof high acoustic impedance metal layer (not shown). This arrangement mayfacilitate suppressing parasitic lateral resonances in operation of theBAW resonator.

In FIG. 2D, an additional intervening high acoustic impedance layer maybe present in multi-layer metal bottom de-tuned acoustic SHF or EHF wavereflector electrode 2013J but is not shown. This additional interveninghigh acoustic impedance layer may be very thin (e.g. thickness about onetenth or less of an acoustic wavelength of the main resonant frequencyof the BAW resonator 2001J). However, in alternative examples,intervening high acoustic impedance layer may be otherwise embodied,e.g., in a very thin additional intervening multi-layer structure (notshown) in which an aggregate thickness of the entire additionalintervening multi-layer structure is about one tenth or less of anacoustic wavelength of the main resonant frequency of the BAW resonator2001J, e.g., various different materials comprising additionalintervening multi-layer structure (not shown) in which an aggregatethickness of the entire additional intervening multi-layer structure isabout one tenth or less of an acoustic wavelength of the main resonantfrequency of the BAW resonator 2001J. As mentioned previously, in bottomde-tuned reflector electrodes 2013J, the first member having therelatively lower acoustic impedance of the first pair may be arrangedsubstantially nearest, e.g. may substantially abut, the firstpiezoelectric layer (e.g. top piezoelectric layer of the BAW resonator,e.g., piezoelectric stack of the BAW resonator). It is theorized thatbecause any intervening layers are so thin (e.g., in aggregate anyintervening multi-layer structures are so thin), despite their presence,there is still facilitation of suppressing parasitic lateral resonancesin operation of the BAW resonator.

As discussed, interposer layers shown in FIG. 1A, and as explicitlyshown in the simplified diagrams of the various resonators shown inFIGS. 2A, 2B, 2C and 2D may be included and interposed between adjacentpiezoelectric layers in the various resonators. Such interposer layersmay laterally extend within the mesa structure of the stack ofpiezoelectric layers a full lateral extent of the stack, e.g., betweenthe etched edge region of the stack and the opposing etched edge regionof the stack. However, in some other alternative bulk acoustic waveresonator structures, interposer layers may be patterned duringfabrication of the interposer layers (e.g., patterned using masking andselective etching techniques during fabrication of the interposerlayers). Such patterned interposer layers need not extend a full lateralextent of the stack (e.g., need not laterally extend to any etched edgeregions of the stack.) For example, FIG. 2E shows another alternativebulk acoustic wave resonator structure 2001K, similar to bulk acousticwave resonator structure 2001J shown in FIG. 2D, but with differences.For example, in the alternative bulk acoustic wave resonator structure2001K shown in FIG. 2E, patterned interposer layers (e.g., firstpatterned interposer layer 261K) may be interposed between sequentialpairs of opposing axis piezoelectric layers (e.g., first patternedinterposer layer 261K may be interposed between a first pair of opposingaxis piezoelectric layers 201K, 202K, and a second pair of opposing axispiezoelectric layers 203K, 204K).

FIG. 2E shows an eighteen piezoelectric layer alternating axis stackarrangement having an active region of the bulk acoustic wave resonatorstructure 2001K sandwiched between overlap of SHF or EHF detunedharmonically tuned top sensor electrode 2015K and multi-layer metalacoustic SHF or EHF wave reflector bottom electrode 2013K. In FIG. 2E,patterned interposer layers (e.g., first patterned interposer layer261K) may be patterned to have extent limited to the active region ofthe bulk acoustic wave resonator structure 2001K sandwiched betweenoverlap of SHF or EHF detuned harmonically tuned top sensor electrode2015K and multi-layer metal acoustic SHF or EHF wave reflector bottomelectrode 2013K. A planarization layer 265K at a limited extent ofmulti-layer metal acoustic SHF or EHF wave reflector bottom electrode2013K may facilitate fabrication of the eighteen piezoelectric layeralternating axis stack arrangement (e.g., stack of eighteenpiezoelectric layers 201K through 218K).

Patterning of interposer layers may be done in various combinations. Forexample, some interposer layers need not be patterned (e.g., may beunpatterned) within lateral extent of the stack of piezoelectric layers(e.g., some interposer layers may extend to full lateral extent of thestack of piezoelectric layers). For example, first interposer layer 261Jshown in FIG. 2D need not be patterned (e.g., may be unpatterned) withinlateral extent of the stack of piezoelectric layers (e.g., firstinterposer layer 261J may extend to full lateral extent of the stack ofpiezoelectric layers). For example, in FIG. 2D interposer layersinterposed between adjacent sequential pairs of normal axis and reverseaxis piezoelectric layers need not be patterned (e.g., may beunpatterned) within lateral extent of the stack of piezoelectric layers(e.g., interposer layers interposed between sequential pairs of normalaxis and reverse axis piezoelectric layers may extend to full lateralextent of the stack of piezoelectric layers). For example in FIG. 2D,first interposer layer 261J interposed between first sequential pair ofnormal axis and reverse axis piezoelectric layers 201J, 202J andadjacent second sequential pair of normal axis and reverse axispiezoelectric layers 203J, 204J need not be patterned within lateralextent of the stack of piezoelectric layers (e.g., first interposerlayer 261J may extend to full lateral extent of the stack ofpiezoelectric layers). In contrast to these unpatterned interposerlayers (e.g., in contrast to unpatterned interposer layer 261J) as shownin FIG. 2D, in FIG. 2E patterned interposer layers (e.g., firstpatterned interposer layer 261K) may be patterned, for example, to haveextent limited to the active region of the bulk acoustic wave resonatorstructure 2001K shown in FIG. 2E. FIG. 2E shows sensing region 216Jacoustically coupled with SHF or EHF detuned harmonically tuned topsensor electrode 2015K.

FIGS. 3A through 3C illustrate example integrated circuit structuresused to form the example bulk acoustic wave resonator structure of FIG.1A. As shown in FIG. 3A, magnetron sputtering may sequentially depositlayers on silicon substrate 101. Initially, a seed layer 103 of suitablematerial (e.g., aluminum nitride (AlN), e.g., silicon dioxide (SiO₂),e.g., aluminum oxide (Al₂O₃), e.g., silicon nitride (Si₃N₄), e.g.,amorphous silicon (a-Si), e.g., silicon carbide (SiC)) may be deposited,for example, by sputtering from a respective target (e.g., from analuminum, silicon, or silicon carbide target). The seed layer may have alayer thickness in a range from approximately one hundred Angstroms (100A) to approximately one micron (1 um). In some examples, the seed layer103 may also be at least partially formed of electrical conductivityenhancing material such as Aluminum (Al) or Gold (Au). Next, successivepairs of alternating layers of high acoustic impedance metal and lowacoustic impedance metal may be deposited by alternating sputtering fromtargets of high acoustic impedance metal and low acoustic impedancemetal. For example, sputtering targets of high acoustic impedance metalsuch as Molybdenum or Tungsten may be used for sputtering the highacoustic impedance metal layers, and sputtering targets of low acousticimpedance metal such as Aluminum or Titanium may be used for sputteringthe low acoustic impedance metal layers. For example, the fourth pair ofbottom metal electrode layers, 133, 131, may be deposited by sputteringthe high acoustic impedance metal for a first bottom metal electrodelayer 133 of the pair on the seed layer 103, and then sputtering the lowacoustic impedance metal for a second bottom metal electrode layer 131of the pair on the first layer 133 of the pair. Similarly, the thirdpair of bottom metal electrode layers, 129, 127, may then be depositedby sequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Similarly, the second pairof bottom metal electrodes 125, 123, may then be deposited bysequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Similarly, the first pairof bottom metal electrodes 121, 119, may then be deposited bysequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Respective layerthicknesses of bottom metal electrode layers of the second, third andfourth pairs 119, 121, 123, 125, 127, 129, 131, 133 may correspond toapproximately a quarter wavelength (e.g., a quarter of an acousticwavelength) of the resonant frequency at the resonator (e.g., respectivelayer thickness of about six hundred Angstroms (660 A) for the example24 GHz resonator.) However, in the figures, the first member 119 of thefirst pair of bottom metal electrode layers for the bottom acousticreflector is depicted as relatively thicker (e.g., thickness of thefirst member 119 of the first pair of bottom metal electrode layers isdepicted as relatively thicker) than thickness of remainder bottomacoustic layers. For example, a thickness of the first member 119 of thefirst pair of bottom metal electrode layers may be about 60 Angstromsgreater, e.g., substantially greater, than an odd multiple (e.g., 1×,3×, etc.) of a quarter of a wavelength (e.g., 60 Angstroms greater thanone quarter of the acoustic wavelength) for the first member 119 of thefirst pair of bottom metal electrode layers. For example, if Titanium isused as the low acoustic impedance metal for a 24 GHz resonator (e.g.,resonator having a main resonant frequency of about 24 GHz), a thicknessfor the first member 119 of the first pair of bottom metal electrodelayers of the bottom acoustic may be about 690 Angstroms, whilerespective layer thicknesses shown in the figures for correspondingmembers of the other pairs of bottom metal electrode layers may besubstantially thinner.

Next, as shown in FIG. 3B, the bottom electrode layers may be patterned(e.g., by photolithographic masking and etching) and planarized, forexample using the planarization material 165. A suitable planarizationmaterial (e.g., Silicon Dioxide (SiO2), Hafnium Dioxide (HfO2),Polyimide, or BenzoCyclobutene (BCB)). These materials may be depositedby suitable methods, for example, chemical vapor deposition, standard orreactive magnetron sputtering (e.g., in cases of SiO2 or HfO2) or spincoating (e.g., in cases of Polyimide or BenzoCyclobutene (BCB)).

FIG. 3C shows that a stack of four layers of piezoelectric material, forexample, four layers of Aluminum Nitride (AlN) having the wurtzitestructure deposited by sputtering. For example, bottom piezoelectriclayer 105, first middle piezoelectric layer 107, second middlepiezoelectric layer 109, and top piezoelectric layer 111 may bedeposited by sputtering. The four layers of piezoelectric material inthe stack 104, may have the alternating axis arrangement in therespective stack 104. For example the bottom piezoelectric layer 105 maybe sputter deposited to have the normal axis orientation, which isdepicted in FIG. 3C using the downward directed arrow. The first middlepiezoelectric layer 107 may be sputter deposited to have the reverseaxis orientation, which is depicted in the FIG. 3C using the upwarddirected arrow. The second middle piezoelectric layer 109 may have thenormal axis orientation, which is depicted in the FIG. 3C using thedownward directed arrow. The top piezoelectric layer may have thereverse axis orientation, which is depicted in the FIG. 3C using theupward directed arrow. As mentioned previously herein, polycrystallinethin film MN may be grown in the crystallographic c-axis negativepolarization, or normal axis orientation perpendicular relative to thesubstrate surface using reactive magnetron sputtering of the Aluminumtarget in the nitrogen atmosphere. As was discussed in greater detailpreviously herein, changing sputtering conditions, for example by addingoxygen, may reverse the axis to a crystallographic c-axis positivepolarization, or reverse axis, orientation perpendicular relative to thesubstrate surface.

Interposer layers may be sputtered between sputtering of piezoelectriclayers, so as to be sandwiched between piezoelectric layers of thestack. For example, first interposer layer 159, may sputtered betweensputtering of bottom piezoelectric layer 105, and the first middlepiezoelectric layer 107, so as to be sandwiched between the bottompiezoelectric layer 105, and the first middle piezoelectric layer 107.For example, second interposer layer 161 may be sputtered betweensputtering first middle piezoelectric layer 107 and the second middlepiezoelectric layer 109 so as to be sandwiched between the first middlepiezoelectric layer 107, and the second middle piezoelectric layer 109.For example, third interposer layer 163, may be sputtered betweensputtering of second middle piezoelectric layer 109 and the toppiezoelectric layer 111 so as to be sandwiched between the second middlepiezoelectric layer 109 and the top piezoelectric layer 111.

As discussed previously, one or more of the interposer layers (e.g.,interposer layers 159, 161, 163) may be metal interposer layers, e.g.,high acoustic impedance metal interposer layers, e.g., Molybdenum metalinterposer layers. These may be deposited by sputtering from a metaltarget. As discussed previously, one or more of the interposer layers(e.g., interposer layers 159, 161, 163) may be dielectric interposerlayers, e.g., silicon dioxide interposer layers. These may be depositedby reactive sputtering from a Silicon target in an oxygen atmosphere.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be formed of different metal layers. For example,high acoustic impedance metal layer such as Tungsten (W), Molybdenum(Mo) may (but need not) raise effective electromechanical couplingcoefficient (Kt2) while subsequently deposited metal layer withhexagonal symmetry such as Titanium (Ti) may (but need not) facilitatehigher crystallographic quality of subsequently deposited piezoelectriclayer. Alternatively or additionally, one or more (e.g., one or aplurality of) interposer layers may be formed of different dielectriclayers.

For example, high acoustic impedance dielectric layer such as HafniumDioxide (HfO2) may (but need not) raise effective electromechanicalcoupling coefficient (Kt2). Subsequently deposited amorphous dielectriclayer such as Silicon Dioxide (SiO2) may (but need not) facilitatecompensating for temperature dependent frequency shifts. Alternativelyor additionally, one or more (e.g., one or a plurality of) interposerlayers may comprise metal and dielectric for respective interposerlayers. For example, high acoustic impedance metal layer such asTungsten (W), Molybdenum (Mo) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2). Subsequently depositedamorphous dielectric layer such as Silicon Dioxide (SiO2) may (but neednot) facilitate compensating for temperature dependent frequency shifts.Sputtering thickness of interposer layers may be as discussed previouslyherein. Interposer layers may facilitate sputter deposition ofpiezoelectric layers. For example, initial sputter deposition of secondinterposer layer 166 on reverse axis first middle piezoelectric layer107 may facilitate subsequent sputter deposition of normal axispiezoelectric layer 109.

Similar to the previous discussion of patterning, etching andplanarization in forming the bottom electrode layers of multilayer metalacoustic reflector electrode 113, the stack 104 of four piezoelectriclayers 105, 107, 109, 111 and their interposers may be patterned (e.g.,by photolithographic masking and etching) and planarized.

The harmonically tuned top sensor electrode 115 may be deposited bysputtering the high acoustic impedance metal onto the stack 104 of fourpiezoelectric layers 105, 107, 109, 111. Thickness of the harmonicallytuned top electrode 115 may be approximately an integral multiple of ahalf of an acoustic wavelength (e.g., one wavelength) of the resonantfrequency of the BAW resonator coupled with the sensing region. Theharmonically tuned top sensor electrode 115 may be patterned (e.g., byphotolithographic masking and etching) and planarized. In aggregate, theetching of harmonically tuned top sensor electrode 115, the etching ofthe stack 104 of four piezoelectric layers 105, 107, 109, 111, and theetching of multilayer metal acoustic reflector electrode 113 for etchededge region 153 extending there through as shown in FIG. 3C. A notionalheavy dashed line is used in FIG. 3C depicting the etched edge region153 associated with the harmonically tuned top sensor electrode 115. Afirst portion of etched edge region 153 may extend along the thicknessdimension T25 of the harmonically tuned top sensor electrode 115. Themesa structure (e.g., third mesa structure) corresponding to theharmonically tuned top sensor electrode 115 may extend laterally between(e.g., may be formed between) etched edge region 153 and laterallyopposing etched edge region 154. Dry etching may be used, e.g., reactiveion etching may be used to etch the materials of the harmonically tunedtop sensor electrode 115. Chlorine based reactive ion etch may be usedto etch Aluminum, in cases where Aluminum is used in the harmonicallytuned top sensor electrode 115. Fluorine based reactive ion etch may beused to etch Tungsten (W), Molybdenum (Mo), Titanium (Ti), SiliconNitride (SiN), Silicon Dioxide (SiO2) and/or Silicon Carbide (SiC) incases where these materials are used in the harmonically tuned topsensor electrode 115.

An isolation layer 167 may also be included and arranged over theplanarization layer 165. For the acoustic resonator based sensor of thisdisclosure, a suitable dielectric material may be used for the isolationlayer 167, for example Silicon Nitride, Silicon Dioxide, or AluminumNitride. Thickness of isolation layer 167 may be controlled, forexample, to be very thin, for example, within a range from approximatelyfifty Angstroms to approximately three hundred Angstroms (approximately50 A to approximately 300 A) for resonators designed to operate atapproximately 24 GHz. After planarization layer 165 (e.g., in one ormore steps) and the isolation layer 167 have been deposited, additionalprocedures of photolithographic masking, layer etching, and mask removalmay be done to form a pair of etched acceptance locations 183A, 183B forelectrical interconnections. Reactive ion etching or inductively coupledplasma etching with a gas mixture of argon, oxygen and a fluorinecontaining gas such as tetrafluoromethane (CF4) or Sulfur hexafluoride(SF6) may be used to etch through the isolation layer 167 and theplanarization layer 165 to form the pair of etched acceptance locations183A, 183B for electrical interconnections. Photolithographic masking,sputter deposition, and mask removal may then be used form electricalinterconnects in the pair of etched acceptance locations 183A, 183Bshown in FIG. 3C, so as to provide for the bottom electricalinterconnect 169 and top electrical interconnect 171 that are shownexplicitly in FIG. 1A. A suitable material, for example Gold (Au) orcopper (CU) may be used for the bottom electrical interconnect 169 andtop electrical interconnect 171.

FIGS. 4A through 4C show alternative example bulk acoustic waveresonators 400A through 400C to the example bulk acoustic wave resonator100A shown in FIG. 1A. For example, the bulk acoustic wave resonator400A shown in FIG. 4A may have a cavity 483A e.g., an air cavity 483Ae.g., extending into substrate 401A e.g., extending into siliconsubstrate 401A e.g., arranged below multilayer metal acoustic reflectorelectrode 413A. The cavity 483A may be formed using techniques known tothose with ordinary skill in the art. For example, the cavity 483A maybe formed by initial photolithographic masking and etching of thesubstrate 401A (e.g., silicon substrate 401A), and deposition of asacrificial material (e.g., phosphosilicate glass (PSG)). Thephosphosilicate glass (PSG) may comprise 8% phosphorous and 92% silicondioxide. The resonator 400A may be formed over the sacrificial material(e.g., phosphosilicate glass (PSG)). The sacrificial material may thenbe selectively etched away beneath the resonator 400A, leaving cavity483A, beneath the resonator 400A. For example phosphosilicate glass(PSG) sacrificial material may be selectively etched away byhydrofluoric acid beneath the resonator 400A leaving cavity 483A beneaththe resonator 400A. The cavity 483A may, but need not, be arranged toprovide acoustic isolation of the structures, e.g., multilayer metalacoustic reflector electrode 413A, e.g., stack 404A of piezoelectriclayers, e.g., resonator 400A, from the substrate 401A.

Similarly, in FIGS. 4B, 4C, a via 485B, 485C (e.g., through silicon via485B, e.g., through silicon carbide via 485C) may, but need not, bearranged to provide acoustic isolation of the structures, e.g.,multilayer metal acoustic reflector electrode 413B, 413C e.g., stack404B, 404C, of piezoelectric layers, e.g., resonator 400B, 400C from thesubstrate 401B, 401C. The via 485B, 485C, (e.g., through silicon via485B, e.g., through silicon carbide via 485C) may be formed usingtechniques (e.g., using photolithographic masking and etchingtechniques) known to those with ordinary skill in the art. For example,in FIG. 4B, backside photolithographic masking and etching techniquesmay be used to form the through silicon via 485B, and an additionalpassivation layer 487B may be deposited, after the resonator 400B isformed. For example, in FIG. 4C, backside photolithographic masking andetching techniques may be used to form the through silicon carbide via485C, after the harmonically tuned top sensor electrode 415C, and stack404C, of piezoelectric layers are formed. In FIG. 4C, after the throughsilicon carbide via 485C is formed, backside photolithographic maskingand deposition techniques may be used to form multilayer metal acousticreflector electrode 413C, and additional passivation layer 487C.

In FIGS. 4A, 4B, 4C, multilayer metal acoustic reflector electrode 413A,413B, 413C, may include the acoustically reflective bottom electrodestack of the plurality of bottom metal electrode layers, in whichthicknesses of the bottom metal electrode layers may be related towavelength (e.g., acoustic wavelength) at the main resonant frequency ofthe example resonator 400A, 400B, 400C. Respective layer thicknesses,(e.g., T02 through T04, explicitly shown in FIGS. 4A, 4B, 4C) formembers of the pairs of bottom metal electrode layers may be about onequarter of the wavelength (e.g., one quarter acoustic wavelength) at themain resonant frequency of the example resonators 400A, 400B, 400C.Relatively speaking, in various alternative designs of the exampleresonators 400A, 400B, 400C, for relatively lower main resonantfrequencies (e.g., five Gigahertz (5 GHz)) and having correspondingrelatively longer wavelengths (e.g., longer acoustic wavelengths), mayhave relatively thicker bottom metal electrode layers in comparison toother alternative designs of the example resonators 400A, 400B, 400C,for relatively higher main resonant frequencies (e.g., twenty-fourGigahertz (24 GHz)). There may be corresponding longer etching times toform, e.g., etch through, the relatively thicker bottom metal electrodelayers in designs of the example resonator 400A, 400B, 400C, forrelatively lower main resonant frequencies (e.g., five Gigahertz (5GHz)). Accordingly, in designs of the example resonators 400A, 400B,400C, for relatively lower main resonant frequencies (e.g., fiveGigahertz (5 GHz)) having the relatively thicker bottom metal electrodelayers, there may (but need not) be an advantage in etching time inhaving a relatively fewer number (e.g., four (4)) of bottom metalelectrode layers, shown in 4A, 4B, 4C, in comparison to a relativelylarger number (e.g., eight (8)) of bottom metal electrode layers, shownin FIG. 1A. The relatively larger number (e.g., eight (8)) of bottommetal electrode layers, shown in FIG. 1A may (but need not) provide forrelatively greater acoustic isolation than the relatively fewer number(e.g., four (4)) of bottom metal electrode layers. However, in FIGS. 4Aand 4E the cavity 483A, 483E, (e.g., air cavity 483A, 483E) may (butneed not) be arranged to provide acoustic isolation enhancement relativeto some designs without the cavity 483A. Similarly, in FIGS. 4B, 4C, thevia 483B, 483C, (e.g., through silicon via 485B, e.g., through siliconcarbide via 485C) may (but need not) be arranged to provide acousticisolation enhancement relative to some designs without the via 483B,483C.

In FIG. 4A, the cavity 483A may (but need not) be arranged to compensatefor relatively lesser acoustic isolation of the relatively fewer number(e.g., four (4)) of bottom metal electrode layers. In FIG. 4A, thecavity 483A may (but need not) be arranged to provide acoustic isolationbenefits, while retaining possible electrical conductivity improvementsand etching time benefits of the relatively fewer number (e.g., four(4)) of bottom metal electrode layers, e.g., particularly in designs ofthe example resonator 400A for relatively lower main resonantfrequencies (e.g., five Gigahertz (5 GHz)). Similarly, in FIGS. 4B, 4C,the via 483B, 483C, may (but need not) be arranged to compensate forrelatively lesser acoustic isolation of the relatively fewer number(e.g., four (4)) of bottom metal electrode layers. In FIGS. 4B, 4C, thevia 483B, 483C, may (but need not) be arranged to provide acousticisolation benefits, while retaining possible electrical conductivityimprovement benefits and etching time benefits of the relatively fewernumber (e.g., four (4)) of bottom metal electrode layers, e.g.,particularly in designs of the example resonator 400B, 400C, forrelatively lower main resonant frequencies (e.g., five Gigahertz (5GHz), e.g., below six Gigahertz (6 GHz), e.g., below five Gigahertz (5GHz)).

Although in various example resonators, 100A, 400A, 400B,polycrystalline piezoelectric layers (e.g., polycrystalline AluminumNitride (AlN)) may be deposited (e.g., by sputtering), in anotherexample resonator 400C, alternative single crystal or near singlecrystal piezoelectric layers (e.g., single/near single crystal AluminumNitride (AlN)) may be deposited (e.g., by metal organic chemical vapordeposition (MOCVD)). Normal axis piezoelectric layers (e.g., normal axisAluminum Nitride (AlN) piezoelectric layers) may be deposited by MOCVDusing techniques known to those with skill in the art. As discussedpreviously herein, the interposer layers may be deposited by sputtering,but alternatively may be deposited by MOCVD. Reverse axis piezoelectriclayers (e.g., reverse axis Aluminum Nitride (AlN) piezoelectric layers)may likewise be deposited via MOCVD. For the example resonators 400Cshown in FIG. 4C, the alternating axis piezoelectric stack 404Ccomprised of piezoelectric layers 405C, 407C, 409C, 411C, as well asinterposer layers 459C, 461C, 463C, extending along stack thicknessdimension T27 fabricated using MOCVD on a silicon carbide substrate401C. For example, aluminum nitride of piezoelectric layers 405C, 407C,409C, 411C, may grow nearly epitaxially on silicon carbide (e.g., 4HSiC) by virtue of the small lattice mismatch between the polar axisaluminum nitride wurtzite structure and specific crystal orientations ofsilicon carbide. Alternative small lattice mismatch substrates may beused (e.g., sapphire, e.g., aluminum oxide). By varying the ratio of thealuminum and nitrogen in the deposition precursors, an aluminum nitridefilm may be produced with the desired polarity (e.g., normal axis, e.g.,reverse axis). For example, normal axis aluminum nitride may besynthesized using MOCVD when a nitrogen to aluminum ratio in precursorgases approximately 1000. For example, reverse axis aluminum nitride maysynthesized when the nitrogen to aluminum ratio is approximately 27000.In accordance with the foregoing, FIG. 4C shows MOCVD synthesized normalaxis piezoelectric layer 405C, MOCVD synthesized reverse axispiezoelectric layer 407C, MOCVD synthesized normal axis piezoelectriclayer 409C, and MOCVD synthesized reverse axis piezoelectric layer 411C.For example, normal axis piezoelectric layer 405C may be synthesized byMOCVD in a deposition environment where the nitrogen to aluminum gasratio is relatively low, e.g., 1000 or less. Next an oxyaluminum nitridelayer, 459C at lower temperature, may be deposited by MOCVD that mayreverse axis (e.g., reverse axis polarity) of the growing aluminumnitride under MOCVD growth conditions, and has also been shown to beable to be deposited by itself under MOCVD growth conditions. Increasingthe nitrogen to aluminum ratio into the several thousands during theMOCVD synthesis may enable the reverse axis piezoelectric layer 407C tobe synthesized. Interposer layer 461C may be an oxide layer such as, butnot limited to, aluminum oxide or silicon dioxide. This oxide layer maybe deposited in a low temperature physical vapor deposition process suchas sputtering or in a higher temperature chemical vapor depositionprocess. Normal axis piezoelectric layer 409C may be grown by MOCVD ontop of interposer layer 461C using growth conditions similar to thenormal axis layer 405C as discussed previously, namely MOCVD in adeposition environment where the nitrogen to aluminum gas ratio isrelatively low, e.g., 1000 or less. Next an aluminum oxynitride,interposer layer 463C may be deposited in a low temperature MOCVDprocess followed by a reverse axis piezoelectric layer 411C synthesizedin a high temperature MOCVD process and an atmosphere of nitrogen toaluminum ratio in the several thousand range. Upon conclusion of thesedepositions, the piezoelectric stack 404C shown in FIG. 4C may berealized.

FIG. 5 shows a simplified top plan view of an example fluidic system5000A of this disclosure, along with a simplified cross sectional viewof the fluidic system 5000B showing operation of an example bulkacoustic wave resonator structure 500B and sensing region 516A, 516B ofthis disclosure. Top plan view of fluidic system 5000A shows resonatorelectrical interconnects 569A, 569B extending through isolation layer567A. Fluid containment member 550A (e.g., microfluidic containment550A) provides for fluid circulation there through, for example, byincluding fluid entrance aperture 552A (e.g., microfluidic entranceaperture 552A) to provide for fluid entering an inner fluid lumen offluid containment member 550A, and by including fluid exit aperture 554A(e.g., microfluidic exit aperture 554A) to provide for fluid exiting theinner fluid lumen of fluid containment member 550A. Top plan view offluidic system 5000A shows lateral support features 564A as visiblethrough fluid entrance aperture 552A and fluid exit aperture 554A. Topplan view of fluidic system 5000A shows a dashed line rectanglerepresentatively illustrating sensing region 516A associated with thebulk acoustic wave resonator structure disposed proximate a surface ofthe inner fluid lumen of fluid containment member 550A.

Sensing region 516A may have a sensing area within a range fromapproximately sixteen hundred square microns to approximately twentyfive thousand six hundred square microns. Sensing region 516A may have asensing area of approximately sixty four hundred square microns. Sensingregion 516A may have a width dimension W of approximately forty (40)microns wide. Sensing region 516A may have a length dimension L ofapproximately one hundred sixty (160) microns long. These width andlength dimensions of sensing region 516A may accommodate a microfluidicchannel of the inner fluid lumen of fluid containment member 550A.Dimensions of the bulk acoustic wave resonator associated with sensingregion 516A may be sized to approximately accommodate the dimensions ofsensing region 516A.

FIG. 5 shows simplified cross sectional view of the fluidic system 5000Bshowing operation of the example bulk acoustic wave resonator structure500B and sensing region 516B. Cross sectional view of fluidic system5000B shows resonator electrical interconnects 569B, 569B extendingthrough isolation layer 567B. Fluid containment member 550B (e.g.,microfluidic containment 550B) may provide for fluid circulation therethrough, for example, by including fluid entrance aperture 552B (e.g.,microfluidic entrance aperture 552B) to provide for fluid entering theinner fluid lumen of fluid containment member 550B, and by includingfluid exit aperture 554B (e.g., microfluidic exit aperture 554B) toprovide for fluid exiting the inner fluid lumen of fluid containmentmember 550B. Fluid circulation through fluid containment member 550B isdepicted using a downward pointing dark arrow at fluid entrance aperture552B, a horizontal dark arrow extending laterally through the innerfluid lumen (e.g., microfluidic channel) of fluid containment member550B, and an upward pointing dark arrow at fluid exit aperture 554B.Target analytes, depicted using solid black triangles may be suspendedin the fluid flow (e.g. liquid flow, e.g., liquid flow comprisingwater), along with other particles (e.g., un-targeted particle)depicted. Functionalized layer 568B may comprise antibodies targeted forbinding with the target analytes (e.g., target antigens) suspended inthe circulation of the fluid flow through the inner lumen (e.g.,microfluidic channel) of fluid containment member 550B. Surface featuresof the antibodies conform to complementary surface features of targetanalytes (e.g., target antigens) to facilitate selectivity in binding ofthe antibodies with target analytes (e.g., target antigens). This isrepresentatively illustrated in the cross sectional view of fluidicsystem 5000B by the surface features of antibodies being depicted withangled surface features, and by the target analytes (e.g., targetantigens) being depicted with complementary, e.g., triangular, surfacefeatures. For example, the antibodies depicted in FIG. 5 may becoronavirus antibodies, the target antigens may be coronavirus, and thefluid flow may be liquid derived from a blood sample from an infectedpatient.

Cross sectional view of fluidic system 5000B shows lateral supportfeatures 564B. The cross sectional view of fluidic system 5000B showssensing region 516B associated with the bulk acoustic wave resonatorstructure 500B disposed proximate a surface of the inner fluid lumen offluid containment 550B. Details of the bulk acoustic wave resonatorstructure 500B have already been discussed in detail with referencesimilar bulk acoustic resonator 100 shown in FIG. 1A. Accordingly, thebulk acoustic wave resonator structure 500B is only briefly discussedhere. As shown in FIG. 5 , bulk acoustic wave resonator structure 500Bmay comprise a stack of alternating axis piezoelectric layers 504Bsandwiched between multilayer metal acoustic reflector electrode 513Band harmonically tuned top sensor electrode 515B.

Top sensor electrode 515B may be a harmonically tuned top sensorelectrode 515B, e.g., may have a thickness of approximately an integralmultiple of a half acoustic wavelength of the main resonant frequency ofBAW resonator 500B, e.g., e.g., may have a thickness of approximatelyN*λ/2 where N is an integer. For example, harmonically tuned top sensorelectrode 515B may have a thickness of approximately a half acousticwavelength of the main resonant frequency of BAW resonator 500B. Forexample, harmonically tuned top sensor electrode 515B may have athickness of approximately an acoustic wavelength of the main resonantfrequency of BAW resonator 500B. Top sensor electrode 515B may be anon-harmonically tuned top sensor electrode 515B, e.g., may have athickness that is not approximately an integral multiple of a halfacoustic wavelength of the main resonant frequency of BAW resonator500B. For example, in a case where top sensor electrode 515B may be anon-harmonically tuned top sensor electrode 515B, top sensor electrode515B may have a thickness that is approximately a tenth (0.1) of anacoustic wavelength of the main resonant frequency of BAW resonator500B. Top sensor electrode 515B may have thickness that may be within arange from approximately one tenth of the acoustic wavelength of themain resonant frequency of BAW resonator 500B to approximately oneacoustic wavelength of the main resonant frequency of BAW resonator500B.

Planarization material 568B may be used to electrically insulateharmonically tuned top sensor electrode 515B from bottom electricalinterconnect 569B. Bottom electrical interconnect 569B may beelectrically coupled with multilayer metal acoustic reflector electrode513B. Top electrical interconnect 571B may be electrically coupled withharmonically tuned top sensor electrode 515B. The stack of alternatingaxis piezoelectric layers 504B may be electrically and acousticallycoupled with the multilayer metal acoustic reflector electrode 513B andthe harmonically tuned top sensor electrode 504B to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode,e.g., thickness extensional main resonance mode) of BAW resonator 500Bacoustically coupled with the sensing region 516B at the resonantfrequency (e.g., main resonant frequency). For example, such excitationmay be done by using the multilayer metal acoustic reflector electrode513B and the harmonically tuned top sensor electrode 515B to apply anoscillating electric field having a frequency corresponding to theresonant frequency (e.g., main resonant frequency) of the BAW resonator500B acoustically coupled with the sensing region 516B.

Sensing region 516A, 516B may comprise a functionalized layer tofacilitate binding to an analyte. For example, the functionalized layermay comprise antibodies. The functionalized layer of sensing region516A, 516B may comprise a self-assembled monolayer. The functionalizedlayer of sensing region 516A, 516B may comprise one or more bindingbiomolecules (e.g., antibodies) configured to bind with targetbiomolecules (e.g., antigens, e.g., coronavirus). For example,antibodies of the functionalized layer acoustically coupled with bulkacoustic wave resonator 500B at the sensing region 516B may selectivelybind the mass of one or more analytes (e.g., antigens, e.g.,coronavirus). The mass of one or more antigens (e.g., coronavirus)binding to antibodies of the functionalized layer acoustically coupledwith bulk acoustic wave resonator 500B may cause detectable resonancefrequency shifts (e.g., decrease in resonance frequency) in operation ofbulk acoustic wave resonators 500B in its thickness extensional mainresonant mode. Electrical circuitry may be coupled with bulk acousticwave resonator 500B to determine the resonance frequency shift. This maydetect the presence of the targeted antigen (e.g., coronavirus).

Further, mass sensitivity may increase with the square of frequency. Thethickness extensional main resonant mode BAW resonator 500B may operatewith resonant frequencies in the Super High Frequency band (e.g.,resonant frequency of 24.25 GHz, or higher bands, e.g., higher resonantfrequencies), and so their mass sensitivity may be much higher thanresonators operating below the Super High Frequency band. Sensitivity isdiscussed in greater detail subsequently herein. Sensitivity of thefluidic system 5000A, 5000B when the sensing region 516A, 516B may beexposed to fluid may be within a range from approximately one half partper million per one hundred attograms to approximately fifty parts permillion per one hundred attograms, e.g., for a sensing area ofapproximately sixty four hundred square microns. Sensitivity of thefluidic system 5000A, 5000B when the sensing region 116 may be exposedto fluid may be within a range from one KiloHertz CentiMeter Squared perNanoGram to approximately two hundred KiloHertz CentiMeter Squared perNanoGram.

As discussed fluid containment member 550B (e.g., microfluidiccontainment 550B) may provide for fluid circulation there through, forexample, by including fluid entrance aperture 552B (e.g., microfluidicentrance aperture 552B) to provide for fluid entering the inner fluidlumen of fluid containment member 550B, and by including fluid exitaperture 554B (e.g., microfluidic exit aperture 554B) to provide forfluid exiting the inner fluid lumen of fluid containment member 550B.The fluid flow may be liquid derived from a blood sample from aninfected patient. The functionalized layer of sensing region 516A, 516Bmay have an affinity for a constituent of blood. For example, thefunctionalized layer of sensing region 516A, 516B may compriseantibodies that may have an affinity for a virus (e.g., antigen)constituent of blood from an infected patient. However, in otherexamples the functionalized layer of sensing region 516A, 516B may havean affinity for a biomarker (e.g., glucose, e.g., prostate specificantigen) constituent of blood from a patient managing a disease (e.g.,diabetes, e.g., prostate cancer).

In another example, fluid containment member 550B may be an insertablehollow microneedle having an inner lumen bore and one or more aperturesto access an interstitial fluid of a patient. The functionalized layerof sensing region 516A, 516B may have an affinity for a biomarker (e.g.,glucose) constituent of interstitial fluid of a patient managing adisease (e.g., diabetes). Microneedles may be desirable because theirsmall size and extremely sharp tip may reduce insertion pain and tissuetrauma to the patient. The length of the microneedles may be kept shortenough to not penetrate to the pain receptors in the inner layers of thepatient's skin. For example microneedle length may be one (1) millimeteror less. The inner lumen bore of the hollow microneedle may, forexample, have a cross-sectional dimension of greater than 25 microns.The inner lumen bore of the hollow microneedle may, for example, have across-sectional dimension of greater than 100 microns. Advantageously,BAW resonators of this disclosure operating at high frequencies (e.g.,24 GHz) may be made small, e.g., with dimensions small enough toaccommodate being disposed in the inner lumen bore of the hollowmicroneedle having access to the interstitial fluid, e.g., the sensingregion 516A, 516B of BAW resonator 500B may contact the interstitialfluid of a patient via the microneedle having access to the interstitialfluid.

Broadly speaking, a fluid need not necessarily be a liquid. Broadlyspeaking air or more particularly a patient's breath may be recognizedas fluid. Accordingly, in another example, a patient's breath, orportions thereof may circulate through fluid containment member 550B.The functionalized layer of sensing region 516A, 516B may have anaffinity for a biomarker (e.g., acetone, e.g., tetrahydrocannabinol(THC)) constituent of a person's breath, which may be associated with aperson's condition (e.g., lipid oxidation, e.g., marijuanaintoxication).

In other examples, air circulating through fluid containment member 550Bmay provide for detection of targeted analytes of interest. For example,in cases where infectious disease carriers may be airborne, tainted airmay be circulated through fluid containment member 550B. Thefunctionalized layer of sensing region 516A, 516B may have an affinityfor airborne infections disease carriers. Sensing region 516A, 516B ofBAW resonator 500B may detect airborne infections disease carriers.Similarly, coughs or sneezes of infected people may give rise torespiratory droplets that include infectious disease carrierconstituents (e.g., coronavirus). The functionalized layer of sensingregion 516A, 516B may have an affinity for infectious disease carrierconstituents (e.g., coronavirus). Sensing region 516A, 516B of BAWresonator 500B may detect infectious disease carrier constituents (e.g.,coronavirus).

In other examples, tainted air circulating through fluid containmentmember 550B may provide for detection of other targeted analytes ofinterest. Polluted air may include particulate matter. Sensing region516A, 516B of BAW resonator 500B may be used to detect particulatematter. Tainted air may include a toxin (e.g., hydrocarbon gas, e.g.,carbon monoxide e.g., a nerve agent). Sensing region 516A, 516B of BAWresonator 500B may detect the toxin. Tainted air may include a toxin(e.g., hydrocarbon gas, e.g., carbon monoxide e.g., a nerve agent).Sensing region 516A, 516B of BAW resonator 500B may detect the toxin.Tainted air may include volatile organic compounds (e.g., hydrocarbons,e.g., alcohols, e.g., ammonia, e.g., acetone, e.g., ketones, e.g.,aldehydes, e.g., esters, e.g., heterocycles). Sensing region 516A, 516Bof BAW resonator 500B may detect volatile organic compounds. Further,tainted air may be indicative of other dangers. Sensing region 516A,516B of BAW resonator 500B may detect presence of explosives (e.g.,trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX)).

In other examples, air circulating through fluid containment member 550Bmay provide for detection of changes in environmental variables. Sensingregion 516A, 516B of BAW resonator 500B may detect changes inenvironment variables (e.g., changes in air temperature, e.g., changesin air pressure, e.g., changes in air humidity).

In other examples, fluid (e.g., water) circulating through fluidcontainment member 550B may provide for detection of changes in waterquality (e.g., presence of toxins, e.g., presence of heavy metals, e.g.,presence of lead). Sensing region 516A, 516B of BAW resonator 500B maydetect changes in water quality (e.g., presence of toxins, e.g.,presence of heavy metals, e.g., presence of lead).

FIGS. 6A through 6C are simplified diagrams of various exampleresonators of this disclosure, along with respective diagramsillustrating respective corresponding properties as predicted bysimulation. The respective top halves of FIGS. 6A through 6C depictrespective simplified depictions of six BAW resonators: 6001A through6001F in FIG. 6A, 6001I through 6001N in FIG. 6B, and 6001R through6001W in FIG. 6C.

BAW resonators 6001A, 6001I, 60001R comprise respective normal axispiezoelectric layers 601A, 601I, 601R sandwiched between respectivemultilayer metal acoustic reflector electrodes 6013A, 6013I, 6013R andtop sensor electrodes 6015A, 6015I, 6015R.

BAW resonators 6001B, 6001J, 6001S comprise respective two layeralternating arrangements of normal axis piezoelectric layers 601B, 601J,601S and reverse axis piezoelectric layers 602B, 602J, 602S sandwichedbetween respective multilayer metal acoustic reflector electrodes 6013B,6013J, 6013S and top sensor electrodes 6015B, 6015J, 6015S.

BAW resonators 6001C, 6001K, 6001T comprise respective three layeralternating arrangements of normal axis piezoelectric layers 601C, 601K,601T, reverse axis piezoelectric layers 602C, 602K, 602T and secondnormal axis piezoelectric layers 603C, 603K, 603T sandwiched betweenrespective multilayer metal acoustic reflector electrodes 6013C, 6013K,6013T and top sensor electrodes 6015C, 6015K, 6015T.

BAW resonators 6001D, 6001L, 6001U comprise respective four layeralternating arrangements of normal axis piezoelectric layers 601D, 601L,601U, reverse axis piezoelectric layers 602D, 602L, 602U, second normalaxis piezoelectric layers 603D, 603L, 603U and second reverse axispiezoelectric layers 604D, 604L, 604U sandwiched between respectivemultilayer metal acoustic reflector electrodes 6013D, 6013L, 6013U andtop sensor electrodes 6015D, 6015L, 6015U.

BAW resonators 6001E, 6001M, 6001V comprise respective five layeralternating arrangements of normal axis piezoelectric layers 601E, 601M,601V, reverse axis piezoelectric layers 602E, 602M, 602V, second normalaxis piezoelectric layers 603E, 603M, 603V, second reverse axispiezoelectric layers 604E, 604M, 604V, and third normal axispiezoelectric layers 605E, 605M, 605V sandwiched between respectivemultilayer metal acoustic reflector electrodes 6013E, 6013M, 6013V andtop sensor electrodes 6015E, 6015M, 6015V.

BAW resonators 6001F, 6001N, 6001W comprise respective six layeralternating arrangements of normal axis piezoelectric layers 601F, 601N,601W, reverse axis piezoelectric layers 602F, 602N, 602W, second normalaxis piezoelectric layers 603F, 603N, 603W, second reverse axispiezoelectric layers 604F, 604N, 604W, third normal axis piezoelectriclayers 605F, 605N, 605W and third reverse axis piezoelectric layers606F, 606N, 606W sandwiched between respective multilayer metal acousticreflector electrodes 6013F, 6013N, 6013W and top sensor electrodes6015F, 6015N, 6015W.

As shown in FIG. 6A, for BAW resonators 6001A through 6001F, thicknessof top sensor electrodes 6015A through 6015F may vary with N times ahalf acoustic wavelength (λ/2) of BAW resonator resonant frequency, withN being 0.2 or N being 1 or N being 2. Harmonic top sensor electrodeshaving thicknesses that are approximately an integral multiple (e.g.,N=1, e.g., N=2) of a half acoustic wavelength (λ/2) of BAW resonatorresonant frequency may differing performance characteristics relative tonon-harmonic top sensor electrodes having thicknesses that are notapproximately an integral multiple (e.g., N˜0.2) of a half acousticwavelength (λ/2) of BAW resonator resonant frequency. For purposes ofsimulation, BAW resonators 6001A through 6001F are designed to have amain resonant frequency of 24.25 GHz and have a sensing region area atthe top sensor electrodes 6015A through 6015F of approximately 80×80microns. For N being 0.2 the thicknesses of piezoelectric layersabutting the multilayer metal acoustic reflector electrodes 6013Athrough 6013F and top sensor electrodes 6015A through 6015F have beenadjusted in such way that the main resonance frequency of resonators6001A through 6015F is substantially the same as for N being 1 or Nbeing 2.

A lower left diagram 6019G in FIG. 6A shows a normalized (e.g., ratioed)top surface displacement of top sensor electrodes 6015A through 6015F ofBAW resonators 6001A through 6001F versus number of half acousticwavelength (λ/2) alternating axis piezoelectric layers as calculatedfrom finite-element simulations. The displacement of top sensorelectrodes 6015A through 6015F of BAW resonators 6001A through 6001F maycreate a pressure wave in a liquid placed of the top surface andtherefore may lead to Quality factor (Q fractor) loss for resonators6001A through 6001F operating in the thickness extensional mode. Forreference, simulation results of displacement of top sensor electrodes6015A through 6015F of BAW resonators 6001A through 6001F have beennormalized (e.g., ratioed) relative to displacement of top sensorelectrode 6015A for N=0.2 design. Trace 6021G shows that for harmonictop sensor electrodes having thicknesses that are approximately anintegral multiple (e.g., N=1, e.g., N=2) of a half acoustic wavelength(λ/2), as number of alternating axis piezoelectric layers range from onepiezoelectric layer to six piezoelectric layers, normalized ratio of topsurface displacement of top sensor electrodes 6015A through 6015F rangesfrom about 0.8 to 0.1. Trace 6023G shows that for non-harmonic topsensor electrodes having thicknesses that are not approximately anintegral multiple (e.g., N˜0.2) of a half acoustic wavelength (λ/2), asnumber of alternating axis piezoelectric layers range from onepiezoelectric layer to six piezoelectric layers, normalized ratio of topsurface displacement of top sensor electrodes 6015A through 6015F rangesfrom about 1 to 0.1. This shows that increasing number of alternatingaxis piezoelectric layers in BAW resonators 6001A through 6001F from onelayer to six layers correspondingly decreases normalized ratio of topsurface displacement. It is theorized that for a given oscillatingvoltage amplitude applied to the BAW resonators 6001A through 6001F thedisplacement of each piezoelectric layer and therefore the displacementof top sensor electrodes 6015A through 6015F of BAW resonators 6001Athrough 6001F may decrease proportionately to the number of number ofalternating axis piezoelectric layers. Decreasing normalized ratio oftop surface displacement in thickness extensional resonant mode BAWresonators operable in liquid by increasing number of alternating axispiezoelectric layers may be important, since this may limit acousticenergy losses in liquid.

A lower right diagram 6019H in FIG. 6A shows estimated normalized (e.g.,ratioed) energy loss in liquid ratios versus number of half acousticwavelength (λ/2) alternating axis piezoelectric layers. For reference,energy losses in liquid for BAW resonators 6001A through 6001F have beennormalized to energy losses in liquid BAW resonator 6001A with N=0.2non-harmonic top sensing electrode 6015A. It is theorized that energyloss in liquid may be proportional to the body force of top electrode onliquid multiplied by the displacement of top sensor electrodes 6015Athrough 6015F of BAW resonators 6001A through 6001F. Since it istheorized that the body force of top electrode on liquid may beproportional to the squared displacement of top sensor electrode,therefore the energy loss in liquid for the thickness extensional modemay be proportional to the third power of the displacement of top sensorelectrodes 6015A through 6015F of BAW resonators 6001A through 6001F.Trace 6021H shows that for harmonic top sensor electrodes havingthicknesses that are approximately an integral multiple (e.g., N=1,e.g., N=2) of a half acoustic wavelength (λ/2), as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, normalized ratio of loss in liquid for BAWresonators 6001A through 6001F may range from about 0.8 to 0.002. Trace6023H shows that for non-harmonic top sensor electrodes havingthicknesses that are not approximately an integral multiple (e.g.,N˜0.2) of a half acoustic wavelength (λ/2), as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, normalized ratio of loss in liquid for BAWresonators 6001A through 6001F ranges from about 1 to 0.001. This mayindicate that thickness extensional resonant mode BAW resonatorsoperable in liquid with increasing number of alternating axispiezoelectric layers may limit acoustic energy losses in liquid, e.g.,by a factor up to 500 for BAW resonators 6001F with harmonic electrodeshaving N=1 or N=2, and by a factor up to 1000 for BAW resonator 6001Fwith non-harmonic electrode having N=0.2. Notably, the normalizedresults presented in diagrams 6019G and 6019H need not necessarilydepend on specific frequency for which the BAW resonators 6001A through6001F have been designed for, nor the specific sensing area sizes of BAWresonators 6001A through 6001F, as should be appreciated by one skilledin the art, e.g., upon learning from this disclosure.

FIG. 6B shows BAW resonators 6001I through 6001N having non-harmonic topsensor electrodes 6015I through 6015N having thicknesses that are notapproximately an integral multiple (e.g., N˜0.2) of a half acousticwavelength (λ/2) of the resonant frequency of BAW resonators 6001Ithrough 6001N (e.g., non-harmonic top sensor electrodes 6015I through6015N may have thicknesses of 0.1 acoustic wavelength of the resonantfrequency of BAW resonators 6001I through 6001N). For purposes ofsimulation, BAW resonators 6001I through 6001N are designed to have asensing region area at the top sensor electrodes 6015A through 6015F ofapproximately 80×80 microns.

Lower left diagram 60190 and center diagram 6019P of FIG. 6B showsensitivity of BAW resonators 6001I through 6001N versus number of halfacoustic wavelength (λ/2) alternating axis piezoelectric layers forvaried designs of BAW resonators 6001I through 6001N having varied mainresonant frequencies of 4 GHz, 8 GHz and 24.25 GHz. Units of sensitivityfor the lower left diagram 60190 of FIG. 6B are in parts per million perone hundred attograms, e.g., for 80×80 microns squared resonator sensingarea. These units for sensitivity may be particularly helpful forunderstanding sensitivity in terms of virus detection. Electronics maymeasure one part per million or better in frequency shift of resonantfrequency (e.g., delta Fs). A virus, e.g., coronavirus may have a massof 100 attograms in water. Accordingly, the change in mass (delta m) fordetecting one virus, e.g., one coronavirus, binding to an antibody ofthe functionalized layer at the sensing region of the BAW resonator maybe 100 attograms. A sensitivity for a limit of detection for detectingone virus, e.g., one coronavirus may having a mass of 100 attograms inwater, may be one part per million per one hundred attograms, e.g., for80×80 microns squared resonator sensing area (assuming electronicsmeasuring one part per million in frequency shift of resonantfrequency).

Trace 60210 shows sensitivity ranging from about 2 parts per million perone hundred attograms to about 0.35 parts per million per one hundredattograms as number of alternating axis piezoelectric layers range fromone piezoelectric layer to six piezoelectric layers, for BAW resonators6001I through 6001N designed to operate at a main resonant frequency of4 GHz. Trace 60230 shows sensitivity ranging from about 4 parts permillion per one hundred attograms to about 0.7 parts per million per onehundred attograms as number of alternating axis piezoelectric layersrange from one piezoelectric layer to six piezoelectric layers, for BAWresonators 6001I through 6001N designed to operate at a main resonantfrequency of 8 GHz. Trace 60250 shows sensitivity ranging from about 12parts per million per one hundred attograms to about 2.1 parts permillion per one hundred attograms as number of alternating axispiezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001I through 6001N designed tooperate at a main resonant frequency of 24.25 GHz. This diagram 60190may show that BAW resonators operating at high frequency may demonstrateenhanced sensitivity. Moreover, BAW resonators operating at highfrequency may have sufficient sensitivity to detect one virus, e.g., onecoronavirus. This diagram 60190 may also show that although BAWresonators may show decreasing sensitivity as number of alternating axispiezoelectric layers increase, higher frequency resonators may stillretain sufficient sensitivity.

Units of sensitivity for the lower center diagram 6019P of FIG. 6B arein kHz cm{circumflex over ( )}2 per nanogram. These units of sensitivitymay be equivalent to the sensitivity units of parts per million per onehundred attograms, e.g., for 80×80 microns squared resonator sensingarea, used in the other sensitivity diagram 60190 just discussed andshown in the lower left of FIG. 6B. Trace 6021P shows sensitivityranging from about 5 kHz cm{circumflex over ( )}2 per nanogram to about0.9 kHz cm{circumflex over ( )}2 per nanogram as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001I through 6001N designed tooperate at a main resonant frequency of 4 GHz. Trace 6023P showssensitivity ranging from about 20 kHz cm{circumflex over ( )}2 pernanogram to about 3.5 kHz cm{circumflex over ( )}2 per nanogram asnumber of alternating axis piezoelectric layers range from onepiezoelectric layer to six piezoelectric layers, for BAW resonators6001I through 6001N designed to operate at a main resonant frequency of8 GHz. Trace 6025P shows sensitivity ranging from about 180 kHzcm{circumflex over ( )}2 per nanogram to about 32 kHz cm{circumflex over( )}2 per nanogram as number of alternating axis piezoelectric layersrange from one piezoelectric layer to six piezoelectric layers, for BAWresonators 6001I through 6001N designed to operate at a main resonantfrequency of 24.25 GHz.

A lower right diagram 6019Q of FIG. 6B shows a vertical axis of TotalQs, e.g., total quality factor at series resonance including electricalresistance of non-harmonic top sensor electrodes 6015I through 6015Nhaving thicknesses of 0.1 acoustic wavelength of the resonant frequencyof BAW resonators. Notably, the calculation of Total Qs may be performedin two steps. First, two-dimensional finite-element calculations ofQ-factor at series resonance frequency Fs for each BAW resonator 6001Ithrough 6001N having an area corresponding to a 50 ohm resonator designat the respective frequency may be performed, without initiallyaccounting for series resistance of the top sensing electrodes 6015Ithrough 6015N. Second, series resistance of the top sensing electrodes6015I through 6015N may be estimated for one square geometry, and TotalQs may be calculated for a fixed 80×80 microns squared resonator sensingarea. As resonator frequency may increase, there may be an electrodethinning, which may in turn increase electrical resistance and maydecrease Total Qs below what may be required. The lower right diagram6019Q of FIG. 6B shows Total Qs versus number of half acousticwavelength (λ/2) alternating axis piezoelectric layers for varieddesigns of BAW resonators 6001I through 6001N having varied mainresonant frequencies of 4 GHz, 8 GHz and 24.25 GHz.

Trace 6021Q shows Total Qs, e.g., total quality factor at seriesresonance ranging from about 300 to about 1200 as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001I through 6001N designed tooperate at a main resonant frequency of 4 GHz. Trace 6023Q shows TotalQs, e.g., total quality factor at series resonance ranging from about 90to about 400 as number of alternating axis piezoelectric layers rangefrom one piezoelectric layer to six piezoelectric layers, for BAWresonators 6001I through 6001N designed to operate at a main resonantfrequency of 8 GHz. Trace 6025Q shows Total Qs, e.g., total qualityfactor at series resonance ranging from about 4 to about 45 as number ofalternating axis piezoelectric layers range from one piezoelectric layerto six piezoelectric layers, for BAW resonators 6001I through 6001Ndesigned to operate at a main resonant frequency of 24.25 GHz.

The lower right diagram 6019Q of FIG. 6B may show that Total Qs, e.g.,total quality factor may decrease as resonators are designed to operateat higher frequency. However, the lower right diagram 6019Q of FIG. 6Bmay also show that Total Qs, e.g., total quality factor may increase asnumber of alternating axis piezoelectric layers increase, e.g., rangingfrom one piezoelectric layer to six piezoelectric layers. Further, thelower right diagram 6019Q of FIG. 6B may show that Total Qs, e.g., totalquality factor may suffer using non-harmonic electrodes (e.g.,non-harmonic top sensor electrodes 6015I through 6015N havingthicknesses of 0.1 acoustic wavelength). The lower right diagram 6019Qof FIG. 6B may show that Total Qs, e.g., total quality factor may sufferusing non-harmonic electrodes, particularly as BAW resonators aredesigned to operate at higher frequencies. It is theorized that asresonator frequency may increase, there may be an electrode thinning,which may in turn increase electrical resistance and may decrease TotalQs below what may be required.

In FIG. 6C, for BAW resonators 6001R through 6001W, thickness of topsensor electrodes 6015R through 6015W may vary with N times a halfacoustic wavelength (λ/2) of BAW resonator resonant frequency, with Nbeing 0.2 or N being 1 or N being 2. Harmonic top sensor electrodeshaving thicknesses that are approximately an integral multiple (e.g.,N=1, e.g., N=2) of a half acoustic wavelength (λ/2) of BAW resonatorresonant frequency may have differing performance characteristicsrelative to non-harmonic top sensor electrodes having thicknesses thatare not approximately an integral multiple (e.g., N˜0.2) of a halfacoustic wavelength (λ/2) of BAW resonator resonant frequency. Forpurposes of simulation, BAW resonators 6001R through 6001W are designedto have a main resonant frequency of 24.25 GHz and have a sensing regionarea at the top sensor electrodes 6015R through 6015W of approximately80×80 square microns.

Lower left diagram 6019X and center diagram 6019Y of FIG. 6C showsensitivity of BAW resonators 6001R through 6001W versus number of halfacoustic wavelength (λ/2) alternating axis piezoelectric layers forvaried designs of BAW resonators 6001R through 6001W having variedthickness of top sensor electrodes 6015R through 6015W. Units ofsensitivity for the lower left diagram 6019X of FIG. 6C are in parts permillion per one hundred attograms, e.g., for 80×80 square micronsresonator sensing area. As mentioned previously, these units forsensitivity may be particularly helpful for understanding sensitivity interms of virus detection. Electronics may measure one part per millionor better in frequency shift of resonant frequency (e.g., delta Fs). Avirus, e.g., coronavirus may have a mass of 100 attograms in water.Accordingly, the change in mass (delta m) for detecting one virus, e.g.,one coronavirus, binding to an antibody of the functionalized layer atthe sensing region of the BAW resonator may be 100 attograms. Asensitivity for a limit of detection for detecting one virus, e.g., onecoronavirus may having a mass of 100 attograms in water, may be one partper million per one hundred attograms e.g., for 80×80 square micronsresonator sensing area (assuming electronics measuring one part permillion, or better, in frequency shift of resonant frequency).

Trace 6021X shows sensitivity ranging from less than about 6 parts permillion per one hundred attograms to about 2 parts per million per onehundred attograms, e.g., for 80×80 square microns resonator sensingarea, as number of alternating axis piezoelectric layers range from twopiezoelectric layers to six piezoelectric layers, for BAW resonators6001R through 6001W designed for a non-harmonic top sensor electrodehaving a thickness that is not approximately an integral multiple (e.g.,N˜0.2) of a half acoustic wavelength (λ/2) of the resonant frequency ofBAW resonators 6001R through 6001W, (e.g., non-harmonic top sensorelectrodes 6015R through 6015W may have thicknesses of 0.1 acousticwavelength of the resonant frequency of BAW resonators 6001R through6001W). (Total Qs, e.g., total quality factor, may be too low (e.g.,Total Qs of about 4) to provide meaningful data for a one piezoelectriclayer resonator, so it is omitted from Trace 6021X)

Trace 6023X shows sensitivity ranging from about 6 parts per million perone hundred attograms to about 3 parts per million per one hundredattograms, e.g., for 80×80 square microns resonator sensing area, asnumber of alternating axis piezoelectric layers range from onepiezoelectric layer to six piezoelectric layers, for BAW resonators6001R through 6001W designed for harmonic top sensor electrodes havingthicknesses that are approximately one half acoustic wavelength (e.g.,N=1 of a half acoustic wavelength (λ/2)). Trace 6025X shows sensitivityranging from about 4 parts per million per one hundred attograms toabout 2 parts per million per one hundred attograms, e.g., for 80×80square microns resonator sensing area, as number of alternating axispiezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001R through 6001W designedfor harmonic top sensor electrodes having thicknesses that areapproximately one acoustic wavelength (e.g., N=2 of a half acousticwavelength (λ/2)). This diagram 6019X may show that BAW resonatorsoperating at high frequency (e.g., 24.25 GHz may demonstrate relativelyhigh sensitivity. Moreover, BAW resonators operating at high frequencymay have sufficient sensitivity to detect one virus, e.g., onecoronavirus. This diagram 6019X may also show that although BAWresonators may show decreasing sensitivity as number of alternating axispiezoelectric layers increase, relatively high frequency resonators(e.g., 24.25 GHz) may still retain sufficient sensitivity. This diagram6019X may also show that although BAW resonators may show decreasingsensitivity as thickness of top sensor electrodes 6015R through 6015Wmay increase, relatively high frequency resonators (e.g., 24.25 GHz) maystill retain sufficient sensitivity.

Units of sensitivity for the lower center diagram 6019Y of FIG. 6C arein kHz cm{circumflex over ( )}2 per nanogram. These units of sensitivitymay be equivalent to the sensitivity units of parts per million per onehundred attograms, e.g., for 80×80 square microns resonator sensingarea, used in the other sensitivity diagram 6019X just discussed andshown in the lower left of FIG. 6C.

Trace 6021Y shows sensitivity ranging from less than about 95 kHzcm{circumflex over ( )}2 per nanogram to about 30 kHz cm{circumflex over( )}2 per nanogram as number of alternating axis piezoelectric layersrange from two piezoelectric layers to six piezoelectric layers, for BAWresonators 6001R through 6001W designed for a non-harmonic top sensorelectrode having a thickness that is not approximately an integralmultiple (e.g., N˜0.2) of a half acoustic wavelength (λ/2) of theresonant frequency of BAW resonators 6001R through 6001W, (e.g.,non-harmonic top sensor electrodes 6015R through 6015W may havethicknesses of about 0.1 acoustic wavelength of the resonant frequencyof BAW resonators 6001R through 6001W). (Total Qs, e.g., total qualityfactor, may be too low to provide meaningful data for a onepiezoelectric layer resonator, so it is omitted from Trace 6021X)

Trace 6023Y shows sensitivity ranging from about 100 kHz cm{circumflexover ( )}2 per nanogram to about 40 kHz cm{circumflex over ( )}2 pernanogram as number of alternating axis piezoelectric layers range fromone piezoelectric layer to six piezoelectric layers, for BAW resonators6001R through 6001W designed for harmonic top sensor electrodes havingthicknesses that are approximately one half acoustic wavelength (e.g.,N=1 of a half acoustic wavelength (λ/2)). Trace 6025Y shows sensitivityranging from about 60 kHz cm{circumflex over ( )}2 per nanogram to about30 kHz cm{circumflex over ( )}2 per nanogram as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001R through 6001W designed tooperate for harmonic top sensor electrodes having thicknesses that areapproximately one acoustic wavelength (e.g., N=2 of a half acousticwavelength (λ/2)).

A lower right diagram 6019Z of FIG. 6C shows a vertical axis of TotalQs, e.g., total quality factor at series resonance for varied designs ofBAW resonators 6001R through 6001W operating a main resonant frequencyof 24.25 GHz and having varied thickness of top sensor electrodes 6015Rthrough 6015W. Notably, the calculation of Total Qs may be performed intwo steps. First, two-dimensional finite-element calculations ofQ-factor at series resonance frequency Fs for each BAW resonator 6001Rthrough 6001W, e.g., having an area corresponding to 50 ohm design atthe respective frequency may be performed without accounting for seriesresistance of the top sensing electrodes 6015R through 6015W. Second,series resistance of the top sensing electrodes 6015R through 6015W beestimated estimated for one square geometry, and Total Qs may becalculated for a fixed 80×80 microns squared resonator sensing area. Atrelatively high resonator frequency (e.g., 24.25 GHz), there may be anelectrode thinning, which may in turn increase electrical resistance,and may decrease Total Qs below what may be required. The lower rightdiagram 6019Z of FIG. 6C shows Total Qs versus number of half acousticwavelength (λ/2) alternating axis piezoelectric layers for varieddesigns of BAW resonators 6001R through 6001W having varied thickness oftop sensor electrodes 6015R through 6015W.

Trace 6021Z shows Total Qs, e.g., total quality factor at seriesresonance ranging from about 280 to about 540 as number of alternatingaxis piezoelectric layers range from one piezoelectric layer to sixpiezoelectric layers, for BAW resonators 6001R through 6001W designedfor harmonic top sensor electrodes having thicknesses that areapproximately one acoustic wavelength (e.g., N=2 of a half acousticwavelength (λ/2)). Trace 6023Z shows Total Qs, e.g., total qualityfactor at series resonance ranging from about 110 to about 270 as numberof alternating axis piezoelectric layers range from one piezoelectriclayer to six piezoelectric layers, for BAW resonators 6001R through6001W designed for harmonic top sensor electrodes having thicknessesthat are approximately one half acoustic wavelength (e.g., N=1 of a halfacoustic wavelength (λ/2)). Trace 6025Z shows Total Qs, e.g., totalquality factor at series resonance ranging from about 12 to about 45 asnumber of alternating axis piezoelectric layers range from twopiezoelectric layers to six piezoelectric layers, for BAW resonators6001R through 6001W having a thickness that is not approximately anintegral multiple (e.g., N˜0.2) of a half acoustic wavelength (λ/2) ofthe resonant frequency of BAW resonators 6001R through 6001W, (e.g.,non-harmonic top sensor electrodes 6015R through 6015W may havethicknesses of 0.1 acoustic wavelength of the resonant frequency of BAWresonators 6001R through 6001W).

The lower right diagram 6019Z of FIG. 6C may show that Total Qs, e.g.,total quality factor may decrease as resonators are designed to operateat higher frequency. However, the lower right diagram 6019Z of FIG. 6Cmay also show that Total Qs, e.g., total quality factor may increase asnumber of alternating axis piezoelectric layers increase, e.g., rangingfrom one piezoelectric layer to six piezoelectric layers. Further, thelower right diagram 6019Z of FIG. 6C may show that Total Qs, e.g., totalquality factor, may suffer using non-harmonic electrodes (e.g.,non-harmonic top sensor electrodes 6015I through 6015N havingthicknesses of 0.1 acoustic wavelength). The lower right diagram 6019Zof FIG. 6C may show that Total Qs, e.g., total quality factor may sufferusing non-harmonic electrodes, particularly as BAW resonators aredesigned to operate at higher frequencies. It is theorized that asresonator frequency may increase, there may be an electrode thinning,which may in turn increase electrical resistance and may decrease TotalQs below what may be required, unless electrodes are thickened, e.g.,using harmonically tuned top sensor electrodes.

FIGS. 7A and 7B are simplified diagrams of various additional exampleresonators of this disclosure, along with respective diagramsillustrating respective corresponding properties as predicted bysimulation. A top half of FIG. 7A shows BAW resonators 7001A, 7001B,7001C that may comprise respective normal axis piezoelectric layers701A, 701B, 701C sandwiched between respective multilayer metal acousticreflector electrodes 7013A, 7013B, 7013C and top sensor electrodes7015A, 7015B, 7015C. BAW resonators 7001A, 7001B, 7001C may haverespective etched edge regions 753A, 753B, 753C, and respective opposingetched edge regions 754A, 754B, 754C. FIG. 7A shows BAW resonators 7001Athrough 7001C having non-harmonic top sensor electrodes 7015A, 7015B,7015C having thicknesses that are not approximately an integral multiple(e.g., N˜0.2) of a half acoustic wavelength (λ/2) of the resonantfrequency of BAW resonators 7001A through 7001C (e.g., non-harmonic topsensor electrodes 7015A through 7015C may have thicknesses of about 0.1acoustic wavelength of the resonant frequency of BAW resonators 7001Athrough 7001C). Area size of respective sensing regions 716A through716C is varied for corresponding BAW resonators 7001A, 7001B, 7001C. Forexample, sensing region 716A of BAW resonator 7001A may have an areasize of 40×40 microns. Sensing region 716B of BAW resonator 7001B mayhave an area size of 80×80 microns. Sensing region 716C of BAW resonator7001C may have an area size of 160×160 microns.

Diagram 7019D shown in FIG. 7A shows sensitivity of BAW resonators 7001Athrough 7001C versus resonant frequencies of 4 GHz, 8 GHz and 24 GHz forvaried designs of BAW resonators 7001A through 7001C having varied sizesof 40×40 microns (corresponding to BAW resonator 7001A), 80×80 microns(corresponding to resonator 7001B) and 160×160 microns (corresponding toresonator 7001C). Units of sensitivity for diagram 7019D of FIG. 7A arein parts per million per one hundred attograms. These units forsensitivity may be particularly helpful for understanding sensitivity interms of virus detection. Electronics may measure one part per millionor better in frequency shift of resonant frequency (e.g., delta Fs). Avirus, e.g., coronavirus may have a mass of 100 attograms in water.Accordingly, the change in mass (delta m) for detecting one virus, e.g.,one coronavirus, binding to an antibody of the functionalized layer atthe sensing region of the BAW resonator may be 100 attograms. Asensitivity for a limit of detection for detecting one virus, e.g., onecoronavirus may having a mass of 100 attograms in water, may be one partper million per one hundred attograms (assuming electronics measuringone part per million in frequency shift of resonant frequency).

Trace 7021D shows sensitivity ranging from about 2 parts per million perone hundred attograms to about 50 parts per million per one hundredattograms as designs for resonant frequency range through 4 GHz, 8 GHzand 24 GHz, for BAW resonator 7001A having area size of 40×40 microns.

Trace 7023D shows sensitivity ranging from about 2 parts per million perone hundred attograms to about 12 parts per million per one hundredattograms as designs for resonant frequency range through 4 GHz, 8 GHzand 24 GHz, for BAW resonator 7001B having area size of 80×80 microns.

Trace 7025D shows sensitivity ranging from about 0.5 parts per millionper one hundred attograms to about 3 parts per million per one hundredattograms as designs for resonant frequency range through 4 GHz, 8 GHzand 24 GHz, for BAW resonator 7001C having area size of 160×160 microns.

This diagram 7019D may show that BAW resonators operating at highfrequency may demonstrate enhanced sensitivity. Moreover, BAW resonatorsoperating at high frequency may have sufficient sensitivity to detectone virus, e.g., one coronavirus. This diagram 7019D may also show thatalthough BAW resonators may show decreasing sensitivity as area sizeincreases, higher frequency resonators may still retain sufficientsensitivity. It may be desirable, in some ways to increase area size tosome extent, for example to fill a base of a microfluidic channel.Further, increasing area size to some extent, may increase a probabilityof detecting a low concentration analyte quickly. However, in terms ofmaintaining BAW resonator sensitivity, diagram 7019D shows that it maybe desirable to limit increases in sensing region area size. Rather thanincreases in sensing region area size, it may be desirable instead toeffectively increase area by employing an array of BAW resonators, e.g.,having an aggregated increased area size.

A top half of FIG. 7B shows BAW resonators 7001E, 7001F, 7001G designedfor operation at a 24.25 GHz main resonant frequency that may compriserespective normal axis piezoelectric layers 701E, 701F, 701G sandwichedbetween respective multilayer metal acoustic reflector electrodes 7013E,7013F, 7013G and top sensor electrodes 7015E, 7015F, 7015G. BAWresonators 7001E, 7001F, 7001G may have respective etched edge regions753E, 753F, 753CG, and respective opposing etched edge regions 754E,754F, 754G. FIG. 7B shows BAW resonators 7001E through 7001G may havevaried thickness of top sensor electrodes 7015E, 7015F, 7015G. Forexample, BAW resonator 7001E may have varied thickness of its top sensorelectrodes 7015E, but one example of BAW resonator 7001E is shown inFIG. 7B as having a non-harmonic top sensor electrode 7015E having athickness that is not approximately an integral multiple (e.g., N˜0.2)of a half acoustic wavelength (λ/2) of the resonant frequency of BAWresonator 7001E (e.g., one example of BAW resonator 7001E is shown inFIG. 7B as having thicknesses of 0.1 acoustic wavelength of the resonantfrequency of BAW resonator 7001E). The example resonator 7001E shown inFIG. 7B having top electrode thicknesses of 0.1 acoustic wavelength mayhave different piezoelectric layer thickness than the other exampleresonators (e.g., 7001F, 7001G) shown in FIG. 7B having harmonic topelectrodes. For non-harmonic (e.g., 0.1 acoustic wavelength) electrodeexamples, the piezoelectric layer may be sandwiched between top andbottom 0.1 acoustic wavelength electrodes, and the entire thickness ofthe stack of the piezoelectric layer sandwiched between top and bottom0.1 acoustic wavelength electrodes may be about a half acousticwavelength. For example, the piezoelectric layer may be about ninehundred Angstroms thick (900 A thick) and the bottom and top Moelectrodes may be about two hundred seventy Angstroms thick (270 A). Incontrast, example resonators having harmonic top electrodes may havefull half wavelength thick piezoelectric layers, for example, havingthicknesses of about 2200 A each and a bottom multilayer metal acousticreflector electrode. BAW resonator 7001F may have varied thickness ofits top sensor electrodes 7015F, but one example of BAW resonator 7001Fis shown in FIG. 7B as having a harmonic top sensor electrode 7015Fhaving a thickness that is approximately an integral multiple (e.g.,N=1) of a half acoustic wavelength (λ/2) of the resonant frequency ofBAW resonator 7001F (e.g., one example of BAW resonator 7001F is shownin FIG. 7B as having thicknesses of a half acoustic wavelength of theresonant frequency of BAW resonator 7001F). BAW resonator 7001G may havevaried thickness of its top sensor electrodes 7015F, but one example ofBAW resonator 7001G is shown in FIG. 7B as having a harmonic top sensorelectrode 7015G having a thickness that is approximately an integralmultiple (e.g., N=2) of a half acoustic wavelength (λ/2) of the resonantfrequency of BAW resonator 7001G (e.g., one example of BAW resonator7001G is shown in FIG. 7B as having thicknesses of one acousticwavelength of the resonant frequency of BAW resonator 7001G). Area sizeof respective sensing regions 716E through 716G is varied forcorresponding BAW resonators 7001E, 7001F, 7001G. For example, sensingregions 716E through 716G of BAW resonators 7001E through 7001G may havearea sizes ranging from 40×40 microns, through 80×80 microns, andthrough 160×160 microns.

Diagram 7019H shown in FIG. 7B shows sensitivity of BAW resonators(e.g., BAW resonators 7001E through 7000G) versus thickness of topsensor electrodes (e.g., top sensor electrodes 7015E through 7015G) forvaried designs of BAW resonators 7001A through 7001C having variedsensor region area sizes of 40×40 microns, 80×80 microns and 160×160microns. Units of sensitivity for diagram 7019H of FIG. 7B are in partsper million per one hundred attograms. Trace 7021H shows sensitivityranging from about 50 parts per million per one hundred attograms toabout 16 parts per million per one hundred attograms as designs for topsensor electrode thickness ranging through 0.1 acoustic wavelength, onehalf acoustic wavelength, and one acoustic wavelength of the 24.25 GHzBAW resonator, for sensing regions having area size of 40×40 microns.

Trace 7023H shows sensitivity ranging from about 12 parts per millionper one hundred attograms to about 4 parts per million per one hundredattograms as designs for top sensor electrode thickness ranging through0.1 acoustic wavelength, one half acoustic wavelength, and one acousticwavelength of the 24.25 GHz BAW resonator, for sensing regions havingarea size of 80×80 microns.

Trace 7025H shows sensitivity ranging from about 3 parts per million perone hundred attograms to about 1 part per million per one hundredattograms as designs for top sensor electrode thickness ranging through0.1 acoustic wavelength, one half acoustic wavelength, and one acousticwavelength of the 24.25 GHz BAW resonator, for sensing regions havingarea size of 160×160 microns.

This diagram 7019H may show that BAW resonators operating at highfrequency (e.g., 24.25 GHz) may demonstrate enhanced sensitivity.Moreover, BAW resonators operating at high frequency (e.g., 24.25 GHz)may have sufficient sensitivity to detect one virus, e.g., onecoronavirus. This diagram 7019H may also show that although BAWresonators may show decreasing sensitivity as area size increases, highfrequency resonators (e.g., 24.25 GHz) may still retain sufficientsensitivity. Although, increasing thickness of the top sensor electrode,e.g., to one acoustic wavelength may decrease sensitivity somewhat,limiting area size of sensing regions of BAW resonators (e.g., to 80×80microns or 40×40 microns) may still provide very high sensitivity.

FIGS. 8A and 8B show an example oscillator 800A, 800B (e.g., millimeterwave oscillator 800A, 800B, e.g., Super High Frequency (SHF) waveoscillator 800A, 800B, e.g., Extremely High Frequency (EHF) waveoscillator 800A, 800B) using the bulk acoustic wave resonator structureof FIG. 1A. For example, FIGS. 8A and 8B shows simplified views of bulkacoustic wave resonator 801A, 801B and electrical coupling nodes 856A,858A, 856B, 858B that may be electrically coupled with bulk acousticwave resonator 801A, 801B. As shown in FIGS. 8A and 8B, electricalcoupling nodes 856A, 858A, 856B, 858B may facilitate an electricalcoupling of bulk acoustic wave resonator 801A, 801B with electricaloscillator circuitry (e.g., active oscillator circuitry 802A, 802B), forexample, through phase compensation circuitry 803A, 803B (Φcomp). Theexample oscillator 800A, 800B may be a negative resistance oscillator,e.g., in accordance with a one-port model as shown in FIGS. 8A and 8B.The electrical oscillator circuitry, e.g., active oscillator circuitrymay include one or more suitable active devices (e.g., one or moresuitably configured amplifying transistors) to generate a negativeresistance commensurate with resistance of the bulk acoustic waveresonator 801A, 801B. In other words, energy lost in bulk acoustic waveresonator 801A, 801B may be replenished by the active oscillatorcircuitry, thus allowing steady oscillation, e.g., steady SHF or EHFwave oscillation. To ensure oscillation start-up, active gain (e.g.,negative resistance) of active oscillator circuitry 802A, 802B may begreater than one. As illustrated on opposing sides of a notional dashedline in FIGS. 8A and 8B, the active oscillator circuitry 802A, 802B mayhave a complex reflection coefficient of the active oscillator circuitry(Γamp), and the bulk acoustic wave resonator 801A, 801B together withthe phase compensation circuitry 803A, 803B (Φcomp) may have a complexreflection coefficient (Γres). To provide for the steady oscillation,e.g., steady SHF or EHF wave oscillation, a magnitude may be greaterthan one for |Γamp Γres|, e.g., magnitude of a product of the complexreflection coefficient of the active oscillator circuitry (Γamp) and thecomplex reflection coefficient (Γres) of the resonator to bulk acousticwave resonator 801A, 801B together with the phase compensation circuitry803A, 803B (Φcomp) may be greater than one. Further, to provide for thesteady oscillation, e.g., steady SHF or EHF wave oscillation, phaseangle may be an integer multiple of three-hundred-sixty degrees for∠Γamp Γres, e.g., a phase angle of the product of the complex reflectioncoefficient of the active oscillator circuitry (Γamp) and the complexreflection coefficient (Γres) of the resonator to bulk acoustic waveresonator 801A, 801B together with the phase compensation circuitry803A, 803B (Φcomp) may be an integer multiple of three-hundred-sixtydegrees. The foregoing may be facilitated by phase selection, e.g.,electrical length selection, of the phase compensation circuitry 803A,803B (Φcomp).

In the simplified view of FIG. 8A, the bulk acoustic wave resonator 801Amay have a sensing region 816 acoustically coupled with the bulkacoustic wave resonator 801A via a harmonically tuned top sensorelectrode 815A of the bulk acoustic wave resonator 801A. The bulkacoustic wave resonator 801A (e.g., bulk acoustic SHF or EHF waveresonator) includes first normal axis piezoelectric layer 805A, firstreverse axis piezoelectric layer 807A, and another normal axispiezoelectric layer 809A, and another reverse axis piezoelectric layer811A arranged in a four piezoelectric layer alternating axis stackarrangement sandwiched between a detuned SHF or EHF harmonically tunedtop sensor electrode 815A and de-tuned multilayer metal acoustic SHF orEHF wave reflector electrode 813A. General structures and applicableteaching of this disclosure for the detuned SHF or EHF harmonicallytuned top sensor electrode 815A and the de-tuned multilayer metalacoustic SHF or EHF wave reflector electrode 813A have already beendiscussed in detail previously herein with respect of FIGS. 1A and 4Athrough 4C, which for brevity are incorporated by reference rather thanrepeated fully here. As already discussed, the de-tuned multilayer metalacoustic SHF or EHF wave reflector electrode 813A is directed torespective pairs of metal electrode layers, in which a first member ofthe pair has a relatively low acoustic impedance (relative to acousticimpedance of an other member of the pair), in which the other member ofthe pair has a relatively high acoustic impedance (relative to acousticimpedance of the first member of the pair), and in which the respectivepairs of metal electrode layers have layer thicknesses corresponding toone quarter wavelength (e.g., one quarter acoustic wavelength) at a mainresonant frequency of the resonator. Accordingly, it should beunderstood that the bulk acoustic SHF or EHF wave resonator 801A shownin FIG. 8A may include a de-tuned multilayer metal acoustic SHF or EHFwave reflector electrode 813A. Similarly, SHF or EHF harmonically tunedtop sensor electrode 815A may be detuned.

For example, to provide for de-tuning (e.g., tuning up) of the SHF orEHF harmonically tuned top sensor electrode 815A, thickness (e.g., oneacoustic wavelength thickness) of the harmonically tuned top sensorelectrode 815A may be made somewhat thinner. For example, thickness ofthe SHF or EHF harmonically tuned top sensor electrode 815A may be about260 Angstroms lesser, e.g., about 10% thinner than an acousticwavelength corresponding to an example BAW resonator resonant frequencyof 24.25 GHz.

An output 816A of the oscillator 800A may be coupled to the bulkacoustic wave resonator 801A (e.g., coupled to harmonically tuned topsensor electrode 815A). It should be understood that interposer layersas discussed previously herein with respect to FIG. 1A are explicitlyshown in the simplified view the example resonator 801A shown in FIG.8A. Such interposer layers may be included and interposed betweenadjacent piezoelectric layers. For example, a first interposer layer isarranged between first normal axis piezoelectric layer 805A and firstreverse axis piezoelectric layer 807A. For example, a second interposerlayer is arranged between first reverse axis piezoelectric layer 807Aand another normal axis piezoelectric layer 809A. For example, a thirdinterposer is arranged between the another normal axis piezoelectriclayer 809A and another reverse axis piezoelectric layer 811A. Asdiscussed previously herein, such interposer may be metal or dielectric,and may, but need not provide various benefits, as discussed previouslyherein. Alternatively or additionally, one or more (e.g., one or aplurality of) interposer layers may comprise metal and dielectric forrespective interposer layers. For example, high acoustic impedance metallayer such as Tungsten (W) or Molybdenum (Mo) may (but need not) raiseeffective electromechanical coupling coefficient (Kt2). Subsequentlydeposited amorphous dielectric layer such as Silicon Dioxide (SiO2) may(but need not) facilitate compensating for temperature dependentfrequency shifts. Alternatively or additionally, one or more (e.g., oneor a plurality of) interposer layers may be formed of different metallayers. For example, high acoustic impedance metal layer such asTungsten (W) or Molybdenum (Mo) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2) while subsequentlydeposited metal layer with hexagonal symmetry such as Titanium (Ti) may(but need not) facilitate higher crystallographic quality ofsubsequently deposited piezoelectric layer. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different dielectric layers. For example, highacoustic impedance dielectric layer such as Hafnium Dioxide (HfO2) may(but need not) raise effective electromechanical coupling coefficient(Kt2). Subsequently deposited amorphous dielectric layer such as SiliconDioxide (SiO2) may (but need not) facilitate compensating fortemperature dependent frequency shifts.

A notional heavy dashed line is used in depicting an etched edge region853A associated with example resonator 801A. The example resonator 801Amay also include a laterally opposing etched edge region 854A arrangedopposite from the etched edge region 853A. The etched edge region 853A(and the laterally opposing etch edge region 854A) may similarly extendthrough various members of the example resonator 801A of FIG. 8A, in asimilar fashion as discussed previously herein with respect to theetched edge region 253D (and the laterally opposing etch edge region254D) of example resonator 2001D shown in FIG. 2B. As shown in FIG. 8A,a first mesa structure corresponding to the stack of four piezoelectricmaterial layers 805A, 807A, 809A, 811A may extend laterally between(e.g., may be formed between) etched edge region 853A and laterallyopposing etched edge region 854A. A second mesa structure correspondingto multi-layer metal bottom de-tuned acoustic SHF or EHF wave reflectorelectrode 813A may extend laterally between (e.g., may be formedbetween) etched edge region 853A and laterally opposing etched edgeregion 854A. Third mesa structure corresponding to harmonically tunedtop sensor electrode 815A may extend laterally between (e.g., may beformed between) etched edge region 853A and laterally opposing etchededge region 854A.

FIG. 8B shows a schematic of an example circuit implementation of theoscillator shown in FIG. 8A. Active oscillator circuitry 802B mayinclude active elements, symbolically illustrated in FIG. 8B byalternating voltage source 804B (Vs) coupled through negative resistance806B (Rneg), e.g., active gain element 806B, to example bulk acousticwave resonator 801B (e.g., bulk acoustic SHF or EHF wave resonator) viaphase compensation circuitry 803B (Φcomp). The representation of examplebulk acoustic wave resonator 801B (e.g., bulk acoustic SHF or EHF waveresonator) may include passive elements, symbolically illustrated inFIG. 8B by electrode ohmic loss parasitic series resistance 808B (Rs),motional capacitance 810B (Cm), acoustic loss motional resistance 812B(Rm), motional inductance 814B (Lm), static or plate capacitance 816B(Co), and acoustic loss parasitic 818B (Ro). Additionally, a variablemass inductance 814BB (Lmass) is depicted in dashed line to representthe variable mass of an analyte binding to the functionalized layer ofthe sensing region of the BAW resonator. An output 816B of theoscillator 800B may be coupled to the bulk acoustic wave resonator 801B(e.g., coupled to the detuned SHF or EHF harmonically tuned top sensorelectrode of bulk acoustic wave resonator 801B).

FIG. 8C shows an array of eighteen Smith charts showingScattering-parameters (S-parameters, e.g., S11) at various operatingfrequencies corresponding various example BAW resonators having from oneto six piezoelectric layers in alternating piezoelectric axis stackarrangements, and having top electrodes thickness varying from about atenth of the acoustic wavelength of the BAW resonators to one half ofthe acoustic wavelength of the BAW resonators, to one acousticwavelength of the BAW resonators. The Smith charts have been simulatedusing two-dimensional finite element models of resonators, for example,having characteristic impedance of 50 ohm at respective series resonancefrequencies. For example, a first row of Smith charts 870A through 870Finclude respective trances 873A through 873F of Scattering-parameters(S-parameters, e.g., S11) over frequency corresponding to BAW resonatorsof this disclosure having top electrode thickness of about a tenth ofacoustic wavelength (˜0.1λ) of the main resonant frequency of the BAWresonator and having from 1 piezoelectric layer (e.g., Npiezo=1) to anincreasing number alternating axis piezoelectric layers, up to sixalternating axis piezoelectric layers (e.g., Npiezo=6). It is theorizedin this disclosure that uneven artifacts apparent in respective traces873A through 873F of may correspond to parasitic lateral resonances. Itis theorized in this disclosure that increasing number of alternatingaxis piezoelectric layers in BAW resonators of this disclosure mayfacilitate suppressing parasitic lateral resonances. This may beindicated in FIG. 8C by fewer/less uneven artifacts being present intrace 873F (corresponding to a BAW resonator having six alternating axispiezoelectric layers (e.g., Npiezo=6)) relative to more uneven artifactsbeing present in trace 873A (corresponding to a BAW resonator having onepiezoelectric layer (e.g., Npiezo=1)).

For example, a second row of Smith charts 870G through 870L includerespective trances 873G through 873L of Scattering-parameters(S-parameters, e.g., S11) over frequency corresponding to BAW resonatorsof this disclosure having top electrode thickness of about half of anacoustic wavelength (λ/2) of the main resonant frequency of the BAWresonator and having from 1 piezoelectric layer (e.g., Npiezo=1) to anincreasing number alternating axis piezoelectric layers, up to sixalternating axis piezoelectric layers (e.g., Npiezo=6). It is theorizedin this disclosure that uneven artifacts apparent in respective traces873G through 873L may correspond to parasitic lateral resonances. It istheorized in this disclosure that increasing number of alternating axispiezoelectric layers in BAW resonators of this disclosure may facilitatesuppressing parasitic lateral resonances. This may be indicated in FIG.8C by fewer/less uneven artifacts being present in trace 873L(corresponding to a BAW resonator having six alternating axispiezoelectric layers (e.g., Npiezo=6)) relative to more uneven artifactsbeing present in trace 873G (corresponding to a BAW resonator having onepiezoelectric layer (e.g., Npiezo=1)). Further, comparing traces 873Athrough 873F of the first row of Smith charts 870A through 870F totraces 873G through 873L of the second row of Smith charts 870G through870L may show fewer/less uneven artifacts being present in traces 873Gthrough 873L of the second row of Smith charts 870G through 870L,relative to more uneven artifacts being present in traces 873A through873F of the first row of Smith charts 870A through 870F. Accordingly itis theorized in this disclosure that increasing top electrode thickness,e.g., from a tenth of acoustic wavelength (˜0.1λ) to about half of anacoustic wavelength (λ/2) (e.g. increasing thickness to provide aharmonic top electrode) may facilitate suppressing parasitic lateralresonances.

For example, a third row of Smith charts 870M through 870R includerespective trances 873M through 873R of Scattering-parameters(S-parameters, e.g., S11) over frequency corresponding to BAW resonatorsof this disclosure having top electrode thickness of about one acousticwavelength (1λ) of the main resonant frequency of the BAW resonator andhaving from 1 piezoelectric layer (e.g., Npiezo=1) to an increasingnumber alternating axis piezoelectric layers, up to six alternating axispiezoelectric layers (e.g., Npiezo=6). It is theorized in thisdisclosure that uneven artifacts that are decreasingly apparent inrespective traces 873M through 873R may correspond to decreasingparasitic lateral resonances. It is theorized in this disclosure thatincreasing number of alternating axis piezoelectric layers in BAWresonators of this disclosure may facilitate suppressing parasiticlateral resonances. This may be indicated in FIG. 8C by fewer/lessuneven artifacts being present in trace 873R (corresponding to a BAWresonator having six alternating axis piezoelectric layers (e.g.,Npiezo=6)) relative to more uneven artifacts being present in trace 873M(corresponding to a BAW resonator having one piezoelectric layer (e.g.,Npiezo=1)). Further, comparing traces 873G through 873L of the secondrow of Smith charts 870G through 870L to traces 873M through 873R of thethird row of Smith charts 870M through 870R may show fewer/less unevenartifacts being present in traces 873M through 873R of the third row ofSmith charts 870M through 870R, relative to more uneven artifacts beingpresent in traces 873G through 873L of the second row of Smith charts870G through 870R. Accordingly, it is theorized in this disclosure thatincreasing top electrode thickness further, e.g., from about a halfacoustic wavelength (λ/2) to about one acoustic wavelength (1λ) mayfurther facilitate suppressing parasitic lateral resonances.

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example bulk acoustic wave resonators shown in FIG. 1A and FIGS. 4Athrough 4C and the example oscillators shown in FIGS. 8A and 8B. Awidely used standard to designate frequency bands in the microwave rangeby letters is established by the United States Institute of Electricaland Electronic Engineers (IEEE). In accordance with standards publishedby the IEEE, as defined herein, and as shown in FIGS. 9A and 9B areapplication bands as follows: L Band (1 GHz-2 GHz), S Band (2 GHz-4GHz), C Band (4 GHz-8 GHz), X Band (8 GHz-12 GHz), Ku Band (12 GHz-18GHz), K Band (18 GHz-27 GHz), Ka Band (27 GHz-40 GHz), V Band (40 GHz-75GHz), and W Band (75 GHz-110 GHz). FIG. 9A shows a first frequencyspectrum portion 9000A in a range from one Gigahertz (1 GHz) to eightGigahertz (8 GHz), including application bands of L Band (1 GHz-2 GHz),S Band (2 GHz-4 GHz) and C Band (4 GHz-8 GHz). As described subsequentlyherein, the 3rd Generation Partnership Project standards organization(e.g., 3GPP) has standardized various 5G frequency bands. For example,included is a first application band 9010 (e.g., 3GPP 5G n77 band) (3.3GHz-4.2 GHz) configured for fifth generation broadband cellular network(5G) applications. As described subsequently herein, the firstapplication band 9010 (e.g., 5G n77 band) includes a 5G sub-band 9011(3.3 GHz-3.8 GHz). The 3GPP 5G sub-band 9011 includes Long TermEvolution broadband cellular network (LTE) application sub-bands 9012(3.4 GHz-3.6 GHz), 9013 (3.6 GHz-3.8 GHz), and 9014 (3.55 GHz-3.7 GHz).A second application band 9020 (4.4 GHz-5.0 GHz) includes a sub-band9021 for China specific applications. Discussed next are UnlicensedNational Information Infrastructure (UNII) bands. A third applicationband 9030 includes a UNII-1 band 9031 (5.15 GHz-5.25 GHz) and a UNII-2Aband 9032 (5.25 GHz 5.33 GHz). An LTE band 9033 (LTE Band 252) overlapsthe same frequency range as the UNII-1 band 6031. A fourth applicationband 9040 includes a UNII-2C band 9041 (5.490 GHz-5.735 GHz), a UNII-3band 9042 (5.735 GHz-5.85 GHz), a UNII-4 band 9043 (5.85 GHz-5.925 GHz),a UNII-5 band 9044 (5.925 GHz-6.425 GHz), a UNII-6 band 9045 (6.425GHz-6.525 GHz), a UNII-7 band 9046 (6.525 GHz-6.875 GHz), and a UNII-8band 9047 (6.875 GHz-7125 GHz). An LTE band 9048 overlaps the samefrequency range (5.490 GHz-5.735 GHz) as the UNII-3 band 9042. Asub-band 9049A shares the same frequency range as the UNII-4 band 9043.An LTE band 9049B shares a subsection of the same frequency range (5.855GHz-5.925 GHz).

FIG. 9B shows a second frequency spectrum portion 9000B in a range fromeight Gigahertz (8 GHz) to one-hundred and ten Gigahertz (110 GHz),including application bands of X Band (8 GHz-12 GHz), Ku Band (12 GHz-18GHz), K Band (18 GHz-27 GHz), Ka Band (27 GHz-40 GHz), V Band (40 GHz-75GHz), and W Band (75 GHz-110 GHz). A fifth application band 9050includes 3GPP 5G bands configured for fifth generation broadbandcellular network (5G) applications, e.g., 3GPP 5G n258 band 9051 (24.25GHz-27.5 GHz), e.g., 3GPP 5G n261 band 9052 (27.5 GHz-28.35 GHz), e.g.,3GPP 5G n257 band 9053 (26.5 GHz-29.5). FIG. 9B shows an EESS (EarthExploration Satellite Service) band 9051A (23.6 GHz-24 GHz) adjacent tothe 3GPP 5G n258 band 9051 (24.25 GHz-27.5 GHz). As will be discussed ingreater detail subsequently herein, an example EESS notch filter of thepresent disclosure may facilitate protecting the EESS (Earth ExplorationSatellite Service) band 9051A (23.6 GHz-24 GHz) from energy leakage fromthe adjacent 3GPP 5G n258 band 9051 (24.25 GHz-27.5 GHz). For example,this may facilitate satisfying (e.g., facilitate compliance with) aspecification of a standards setting organization, e.g., InternationalTelecommunications Union (ITU) specifications, e.g., ITU-R SM.329Category A/B levels of −20 db W/200 MHz, e.g., 3rd GenerationPartnership Project (3GPP) 5G specifications, e.g., 3GPP 5G, unwanted(out-of-band & spurious) emission levels, worst case of −20 db W/200MHz. Alternatively or additionally, this may facilitate satisfying(e.g., facilitate compliance with) a regulatory requirement, e.g., agovernment regulatory requirement, e.g., a Federal CommunicationsCommission (FCC) decision or requirement, e.g., a European Commissiondecision or requirement of −42 db W/200 MHz for 200 MHz for BaseStations (BS) and −38 db W/200 MHz for User Equipment (UE), e.g.,European Commission Decision (EU) 2019/784 of 14 May 2019 onharmonization of the 24.25-27.5 GHz frequency band for terrestrialsystems capable of providing wireless broadband electroniccommunications services in the Union, published May 16, 2019, which ishereby incorporated by reference in its entirety, e.g., a EuropeanOrganization for the Exploitation of Meteorological Satellites(EUMETSAT) decision, requirement, recommendation or study, e.g., aESA/EUMETSAT/EUMETNET study result of −54.2 db W/200 MHz for BaseStations (BS) and 50.4 db W/200 MHz for User Equipment (UE), e.g., theUnited Nations agency of the World Meteorological Organization (WMO)decision, requirement, recommendation or study, e.g., the WMO decisionof −55 db W/200 MHz for Base Stations (BS) and −51 db W/200 MHz for UserEquipment (UE). These specifications and/or decisions and/orrequirements may be directed to suppression of energy leakage from anadjacent band, e.g., energy leakage from an adjacent 3GPP 5G band, e.g.,suppression of transmit energy leakage from the adjacent 3GPP 5G n258band 9051 (24.250 GHz-27.500 GHz), e.g. limiting of spurious out of n258band emissions. A sixth application band 9060 includes the 3GPP 5G n260band 9060 (37 GHz-40 GHz). A seventh application band 9070 includesUnited States WiGig Band for IEEE 802.11ad and IEEE 802.11ay 9071 (57GHz-71 GHz), European Union and Japan WiGig Band for IEEE 802.11ad andIEEE 802.11ay 9072 (57 GHz-66 GHz), South Korea WiGig Band for IEEE802.11ad and IEEE 802.11ay 9073 (57 GHz-64 GHz), and China WiGig Bandfor IEEE 802.11ad and IEEE 802.11ay 9074 (59 GHz-64 GHz). An eighthapplication band 9080 includes an automobile radar band 9080 (76 GHz-81GHz).

Accordingly, it should be understood from the foregoing that theacoustic wave devices (e.g., resonators, e.g., oscillators) of thisdisclosure may be implemented in the respective application frequencybands just discussed. For example, the layer thicknesses of the detunedharmonically tuned top sensor electrodes and the de-tuned multilayermetal acoustic reflector electrodes and piezoelectric layers inalternating axis arrangement for the example acoustic wave devices(e.g., the example 24 GHz bulk acoustic wave resonators) of thisdisclosure may be scaled up and down as needed to be implemented in therespective application frequency bands just discussed. This is likewiseapplicable to example oscillators (e.g., bulk acoustic wave resonatorbased oscillators) of this disclosure to be implemented in therespective application frequency bands just discussed. The followingexamples pertain to further embodiments for acoustic wave devices,including but not limited to, e.g., bulk acoustic wave resonators, e.g.,bulk acoustic wave resonator based oscillators, and from which numerouspermutations and configurations will be apparent.

Example 1 is a bulk acoustic wave (BAW) resonator comprising asubstrate, a first layer of piezoelectric material having a firstpiezoelectric axis orientation, and a top electrode electrically andacoustically coupled with the first layer of piezoelectric material toexcite a resonance mode at a main resonant frequency of the BAWresonator in a Super High Frequency (SHF) band or Extremely HighFrequency (EHF) band.

Example 2, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3rd GenerationPartnership Project (3GPP) band.

Example 3, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3GPP n77 band9010 as shown in FIG. 9A.

Example 4, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3GPP n79 band9020 as shown in FIG. 9A.

Example 5, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3GPP n258 band9051 as shown in FIG. 9B.

Example 6, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3GPP n261 band9052 as shown in FIG. 9B.

Example 7, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in a 3GPP n260 bandas shown in FIG. 9B.

Example 8, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) S band as shown in FIG. 9A.

Example 9, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) C band as shown in FIG. 9A.

Example 10, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) X band as shown in FIG. 9B.

Example 11, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) Ku band as shown in FIG. 9B.

Example 12, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) K band as shown in FIG. 9B.

Example 13, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) Ka band as shown in FIG. 9B.

Example 14, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) V band as shown in FIG. 9B.

Example 15, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in an Institute ofElectrical and Electronic Engineers (IEEE) W band as shown in FIG. 9B.

Example 16, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-1 band 9031,as shown in FIG. 9A.

Example 17, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-2 A band9032, as shown in FIG. 9A.

Example 18, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-2C band9041, as shown in FIG. 9A.

Example 19, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-3 band 9042,as shown in FIG. 9A.

Example 20, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-4 band 9043,as shown in FIG. 9A.

Example 21, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-5 band 9044,as shown in FIG. 9A.

Example 22, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-6 band 9045,as shown in FIG. 9A.

Example 23, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-7 band 9046,as shown in FIG. 9A.

Example 24, the subject matter of Example 1 optionally includes in whichthe main resonant frequency of the BAW resonator is in UNII-8 band 9047,as shown in FIG. 9A.

Example 25, the subject matter of any one or more of Examples 1 through24 optionally include a sensing region acoustically coupled with the topelectrode.

Example 26, the subject matter of any one or more of Examples 1 through25 optionally include a second layer of piezoelectric material having asecond piezoelectric axis orientation substantially opposing the firstpiezoelectric axis orientation of the first layer of piezoelectricmaterial.

Example 27, the subject matter of any one or more of Examples 1 through26 optionally include in which a sensitivity associated with the BAWresonator is within a range from approximately one half part per millionper one hundred attograms to approximately fifty parts per million perone hundred attograms.

Example 28, the subject matter of any one or more of Examples 1 through27 optionally include in which a sensitivity associated with the BAWresonator is within a range from one KiloHertz CentiMeter Squared perNanoGram to approximately two hundred KiloHertz CentiMeter Squared perNanoGram.

Example 29, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of an analyte.

Example 30, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a biomolecule.

Example 31, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of an infectious agent.

Example 32, the subject matter of any one or more of Examples 1 through31 optionally include in which the BAW resonator is associated withdetection of a virus.

Example 33, the subject matter of any one or more of Examples 1 through32 optionally include in which the BAW resonator is associated withdetection of a coronavirus.

Example 34, the subject matter of any one or more of Examples 1 through33 optionally include in which the BAW resonator is associated withdetection of a SARS-Cov-2 virus.

Example 35, the subject matter of any one or more of Examples 1 through31 optionally include in which the BAW resonator is associated withdetection of bioweapon.

Example 36, the subject matter of any one or more of Examples 1 through31 optionally include in which the BAW resonator is associated withdetection of anthrax.

Example 37, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of a biomarker.

Example 38, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of acetone.

Example 39, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of a prostate specific antigen.

Example 40, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of a cancer biomarker.

Example 41, the subject matter of any one or more of Examples 1 through30 optionally include in which the BAW resonator is associated withdetection of glucose.

Example 42, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of an air pollutant.

Example 43, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of particulate matter.

Example 44, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a toxin.

Example 45, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of carbon monoxide.

Example 46, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a volatile organic compound.

Example 47, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a hydrocarbon gas.

Example 48, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a biological weapon.

Example 49, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a chemical weapon.

Example 50, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a nerve agent.

Example 51, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a Sarin.

Example 52, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a water pollutant.

Example 53, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a heavy metal.

Example 54, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of lead.

Example 55, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a heavy metal.

Example 56, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of an antigen.

Example 57, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of an antibody.

Example 58, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a constituent of blood.

Example 59, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a constituent of interstitial fluid.

Example 60, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a constituent of breadth.

Example 61, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of tetrahydrocannabinol.

Example 62, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of an explosive.

Example 63, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of trinitrotoluene (TNT).

Example 64, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX).

Example 65, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of a chemical associated with a chemical weapon.

Example 66, the subject matter of any one or more of Examples 1 through29 optionally include in which the BAW resonator is associated withdetection of dimethyl methylphosphonate.

Example 67, the subject matter of any one or more of Examples 1 through29 optionally include a functionalized layer acoustically coupled withthe top electrode of the BAW resonator, the functionalized layer havingan selective analyte affinity.

Example 68, the subject matter of any one or more of Examples 1 through29 optionally include a functionalized layer acoustically coupled withthe top electrode of the BAW resonator, the functionalized layer havingan selective analyte binding affinity.

Example 69, the subject matter of any one or more of Examples 1 through29 optionally include a molecularly imprinted polymer layer acousticallycoupled with the top electrode.

Example 70, the subject matter of any one or more of Examples 1 through29 optionally include a metal-organic framework acoustically coupledwith the top electrode.

Example 71, the subject matter of any one or more of Examples 1 through29 optionally include a layer of bacteria acoustically coupled with thetop electrode.

Example 72, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in an environmental variable.

Example 73, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in pressure.

Example 74, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in temperature.

Example 75, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in humidity.

Example 76, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in a flux of neutrons.

Example 77, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of a change in a magnetic field.

Example 78, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of terahertz radiation.

Example 79, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of solar blind ultraviolet light

Example 80, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator is associated withdetection of infrared light.

Example 81, the subject matter of any one or more of Examples 1 through28 optionally include a nanoporous layer acoustically coupled with thetop electrode.

Example 82, the subject matter of any one or more of Examples 1 through28 optionally include a nanocomposite layer acoustically coupled withthe top electrode.

Example 83, the subject matter of any one or more of Examples 1 through28 optionally include a nanostructured layer acoustically coupled withthe top electrode.

Example 84, the subject matter of any one or more of Examples 1 through28 optionally include a magnetostrictive layer acoustically coupled withthe top electrode.

Example 85, the subject matter of any one or more of Examples 1 through28 optionally include a multiferroic layer acoustically coupled with thetop electrode.

Example 86, the subject matter of any one or more of Examples 1 through28 optionally include a magnetoelectric layer acoustically coupled withthe top electrode.

Example 87, the subject matter of any one or more of Examples 1 through28 optionally include a heterostructure layer acoustically coupled withthe top electrode.

Example 88, the subject matter of any one or more of Examples 1 through28 optionally include a perovskite layer acoustically coupled with thetop electrode.

Example 89, the subject matter of any one or more of Examples 1 through28 optionally include magnetostrictive exchange biased multilayersacoustically coupled with the top electrode.

Example 90, the subject matter of any one or more of Examples 1 through28 optionally include antiparallel magnetostrictive exchange biasedmultilayers acoustically coupled with the top electrode.

Example 91, the subject matter of any one or more of Examples 1 through28 optionally include a metallic glass acoustically coupled with the topelectrode.

Example 92, the subject matter of any one or more of Examples 1 through28 optionally include a tunable region acoustically coupled with the topelectrode.

Example 93, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator forms a portion of afilter.

Example 94, the subject matter of any one or more of Examples 1 through28 optionally include in which the BAW resonator forms a portion of atunable filter.

Example 95, the subject matter of any one or more of Examples 1 through94 optionally include in which the top electrode is electrically andacoustically coupled with the first layer of piezoelectric material toexcite a thickness extensional main mode of the BAW resonator.

Example 96, the subject matter of any one or more of Examples 1 through95 optionally include in which the BAW resonator comprises at least oneadditional piezoelectric layer.

Example 97, the subject matter of any one or more of Examples 1 through96 optionally include in which the BAW resonator comprises twoadditional layers of piezoelectric material with alternatingpiezoelectric axis orientations.

Example 98, the subject matter of any one or more of Examples 1 through97 optionally include in which the BAW resonator comprises threeadditional layers of piezoelectric material with alternatingpiezoelectric axis orientations.

Example 99, the subject matter of any one or more of Examples 1 through98 optionally include in which the BAW resonator comprises fouradditional layers of piezoelectric material with alternatingpiezoelectric axis orientations.

Example 100, the subject matter of any one or more of Examples 1 through99 optionally include in which the BAW resonator comprises fiveadditional layers of piezoelectric material with alternatingpiezoelectric axis orientations.

Example 101, the subject matter of any one or more of Examples 1 through100 optionally include in which the top electrode has sheet resistanceof less than one Ohm per square.

Example 102, the subject matter of any one or more of Examples 1 through101 optionally include in which the top electrode a harmonically tunedtop electrode.

Example 103, the subject matter of any one or more of Examples 1 through102 optionally include in which the top electrode has a thickness thatis approximately an integral multiple of a half of an acousticwavelength of the main resonant frequency of the BAW resonator.

Example 104, the subject matter of any one or more of Examples 1 through102 optionally include in which the top electrode has a thickness thatis approximately half an acoustic wavelength of the main resonantfrequency of the BAW resonator.

Example 105, the subject matter of any one or more of Examples 1 through102 optionally include in which the top electrode has a thickness thatis approximately an acoustic wavelength of the main resonant frequencyof the BAW resonator.

Example 106, the subject matter of any, the subject matter of any one ormore of Examples 1 through 105 optionally include in which the BAWresonator is a plurality of BAW resonators.

Example 107, the subject matter of example 106 optionally includes inwhich the plurality of BAW resonators have different respective mainresonant frequencies.

Example 108, the subject matter of any one or more examples 106 through107 optionally include in which differing functionalized layers arecoupled with respective members of the plurality of BAW resonators.

Example 109, the subject matter of any one or more examples 106 through108 optionally include in which differing functionalized layers arecoupled with respective members of the plurality of BAW resonators tofacilitate detection of differing analytes.

Example 110, the subject matter of any one or more examples 106 through109 optionally include in which a member of the plurality of BAWresonators is a reference BAW resonator that is substantially shielded.

Example 111, the subject matter of any one or more examples 106 through110 optionally include in which a plurality of heaters respectively arethermally coupled with respective top electrodes regions of respectiveof BAW resonators.

Example 112, the subject matter of example 111 optionally includes aheaters controller coupled with the plurality of heaters to selectivelyactivate and to selectively deactivate the members of the plurality ofheaters.

Example 113, the subject matter of example 112 optionally includes atiming controller coupled with the heaters controller to control timingof the heaters controller selectively activating and to selectivelydeactivating the members of the plurality of heaters.

Example 114, the subject matter of example 113 optionally includes thetiming controller is coupled with the heaters controller to controlrespective temperatures of the respective top electrodes.

Example 115, the subject matter of example 113 optionally includes thetiming controller is coupled with the heaters controller to controlrespective temperatures of the respective top electrodes to be differentfrom one another.

Example 116, the subject matter of example 113 optionally includes thetiming controller coupled with the heaters controller to controlrespective temperatures of respective functionalized layers coupled withrespective top electrodes, so as to control respective analyteadsorption at the respective functionalized layers.

Example 117, the subject matter of example 113 optionally includes thetiming controller coupled with the heaters controller to vary respectivetemperatures of respective top electrodes over time.

Example 118, the subject matter of any one or more examples 111 through117 optionally include a resonant signals receiver coupled with theplurality of BAW resonators.

Example 119, the subject matter of any one or more examples 111 through117 optionally include a resonant signals receiver wirelessly coupledwith the plurality of BAW resonators.

Example 120, the subject matter of any one or more examples 111 through117 optionally include a frequency sweep signals transmitter coupledwith the plurality of BAW resonators.

Example 121, the subject matter of any one or more examples 111 through117 optionally include a frequency sweep signals transmitter wirelesslycoupled with the plurality of BAW resonators.

Example 122, the subject matter of any one or more examples 111 through121 optionally include a replaceable cartridge supportively coupled withthe plurality of Bulk Acoustic Wave (BAW) resonators.

Example 123, the subject matter of any one or more examples 111 through122 optionally include a computing system coupled with the plurality ofBulk Acoustic Wave (BAW) resonators.

Example 124, the subject matter of example 123 optionally includes thecomputing system having a wireless communication capability.

Example 125, the subject matter of any one or more of examples 1 through124 optionally include wherein the BAW resonator forms a portion offluidic system.

Example 126, the subject matter of any one or more of examples 1 through125 optionally include wherein the BAW resonator forms a portion ofmicrofluidic system.

Example 127, the subject matter of any one or more of examples 1 through124 optionally include a hollow microneedle in which the BAW resonatoris disposed within the hollow microneedle.

FIG. 9C shows a simplified system 9000C employing an array 900C of BAWresonator structures 91 through 9N, 91M through 9NM, through to 91Zthrough 9NZ, for sensing according to this disclosure. As shown in FIG.9C, system 9000C may include a plurality heaters 911 through 91N, 911Mthrough 91NM, through to 911Z through 91NZ that may be thermally coupledwith respective BAW resonator structures 91 through 9N, 91M through 9NM,through to 91Z through 9NZ. The heaters may be electrical heaters. Theheaters may be resistive heaters. Respective heaters may be respectiveresonant heaters, e.g., individually identifiable based on respectiveresonant frequency of respective resonant heaters, e.g., respectivediffering resonant heaters may have respective resonant frequenciesdiffering from one another. Respective heaters may be individuallyaddressable, e.g., based on respective resonant frequency of respectiveresonant heaters. Respective heaters may be wirelessly activatable,e.g., selectively activatable, e.g., selectively activatable based onrespective differing resonant frequencies of respective differingrespective resonant heaters. The heaters may be wirelessly deactivatablee.g., selectively deactivatable, e.g., selectively deactivatable basedon respective differing resonant frequencies of respective differingrespective resonant heaters.

The plurality of heaters (e.g., resonant heaters) may be fabricatedseparately from the plurality of BAW resonators. The plurality ofheaters (e.g., resonant heaters) may be thermally coupled with theplurality of BAW resonators after fabrication. Alternatively, theplurality of heaters (e.g., resonant heaters) may be integrallyfabricated along with the plurality of BAW resonators. The plurality ofheaters (e.g., resonant heaters) may be integrally coupled with theplurality of BAW resonators. Alternatively, the heaters may berecognized as a heating function integral with prolonged operation ofthe plurality of BAW resonators. In other words, operational duration ofthe plurality of BAW resonators may result in heating of the pluralityof BAW resonators. The plurality of heaters may be a plurality heaterfunctions integral with duration of operation of respective BAWresonators and heat produced thereby. By the system 9000C controllingtime duration of operation of the plurality of BAW resonators, heatingof the BAW resonators (e.g., the heating function), may be controlled bythe system 9000C. By the system 9000C controlling time duration ofheating during operation of the plurality of BAW resonators, temperatureof the respective sensing regions of the respective BAW resonators maybe controlled by the system 9000C. By the system 9000C controllingfrequency selective power level of operation of the plurality of BAWresonators, heating of the BAW resonators (e.g., the heating function),may be controlled by the system 9000C. By the system 9000C controllingfrequency selective power level of operation of the plurality of BAWresonators, temperature of the respective sensing regions of therespective BAW resonators may be controlled by the system 9000C.

The BAW resonators of array 900C may be similar to those alreadydiscussed, for example, they may be similar to the BAW resonator shownin FIG. 1A. For example, the BAW resonators of array 900C may includerespective sensing regions and respective functionalized layersacoustically coupled with respective harmonic top senor electrodes,which may be similar to sensing region 116 and functionalized layer 168acoustically coupled with harmonic top senor electrode 115 shown in FIG.1A. For the plurality of BAW resonators of array 900C, respectivesensing regions may comprise respective functionalized layers that aredifferent from one another, e.g., to facilitate respective responses todiffering environmental variables. For the plurality of BAW resonatorsof array 900C, the respective sensing regions may sensing areas may bedifferent sizes from one another, e.g., to facilitate respectivediffering responses to an environmental variable. The plurality of BAWresonators of array 900C may be designed and fabricated having differingpiezoelectric layer thickness, e.g., to have respective resonantfrequencies that are different from one another.

In the system 9000C employing the array 900C of BAW resonators as shownin FIG. 9C, one or more members of the plurality of BAW resonators maybe reference BAW resonators. Reference BAW resonators may besubstantially shielded from one or more environmental variable. It maybe assumed that other members of the plurality of BAW resonators may beunshielded BAW resonators, e.g., substantially unshielded fromenvironmental variables, e.g., to facilitate the unshielded BAWresonators sensing changes in the environmental variables. Noise may bereduced by comparing sensory output of one or more unshielded BAWresonators to output or one or more shielded (reference) BAW resonators.The BAW resonators of array 900C may be used in combination with thefluidic system shown and discussed with respect to FIG. 5 (e.g., the BAWresonators of array 900C shown in FIG. 9C may be used in place of BAWresonator 500B shown in FIG. 5 ).

System 9000C may comprise control circuitry 903. The control circuitry903 may be electrically coupled with the plurality of BAW resonators ofarray 900C. For example, the control circuitry 903 may be wirelesslycoupled with the plurality of BAW resonators of array 900C. The controlcircuitry 903 may comprise a frequency sweep signals transmitter 905,e.g., wirelessly coupled with the plurality of BAW resonators of array900C, e.g., to transmit a sweep of frequency signals, e.g., a sweep offrequency signals comprising the respective differing resonantfrequencies of differing members of the plurality of BAW resonators ofarray 900C, e.g., to stimulate resonant sensing at the respectivediffering resonant frequencies of differing members of the plurality ofBAW resonators of array 900C.

The control circuitry 903 may comprise a resonant signals receiver 907,e.g., wirelessly coupled with the plurality of BAW resonators of array900C, e.g., to receive resonant sensing signals from the plurality ofBAW resonators of array 900C in response to their sensing activation bythe sweep of frequency signals from frequency sweep signals transmitter905. The resonant signals receiver 907 may receive respective signalsdiffering in frequency corresponding to respective differing resonantfrequencies of differing members of the plurality of BAW resonators ofarray 900C. The resonant signals receiver 907 may receive responsiveresonant sensing signals at the respective differing resonantfrequencies of differing members of the plurality of BAW resonators ofarray 900C.

The control circuitry 903 may comprise processing 909 (e.g., a suitableprogrammed microprocessor). The processing 909 may be communicativelycoupled with the frequency sweep signals transmitter 905 and theresonant signals receiver 907. The processing 909 may control operationof the frequency sweep signals transmitter 905. The processing 909 maycontrol operation of the resonant signals receiver 907. The processing909 may receive from the resonant signals receiver 907 the resonantsensing signals of the plurality of BAW resonators of array 900C.

The processing 909 may process these resonant sensing signals. Forexample, processing 909 may use respective frequencies of the resonantsensing signals to identify respective members of the plurality of BAWresonators of array 900C that generated the resonant sensing signals.For example, processing 909 may identify different resonant sensorresponses from different respective members of the plurality of BAWresonators of array 900C e.g., using respective differing resonantfrequencies of BAW resonators of array 900C. In some cases at least aportion of system 9000C may be implemented wirelessly. The processing909 may use respective frequencies of the resonant sensing signals towirelessly identify respective members of the plurality of BAWresonators of array 900C that generated the resonant sensing signals.For example, processing 909 may wirelessly identify different resonantsensor responses from different respective members of the plurality ofBAW resonators of array 900C e.g., using respective differing resonantfrequencies of BAW resonators of array 900C.

The control circuitry 903 may comprise a heaters controller 911. Theheaters controller 911 may be coupled with the processing 909. Theheaters controller 911 may be coupled with the plurality of heaters toselectively activate and to selectively deactivate respective members ofthe plurality of heaters. The control circuitry 903 may comprise atiming controller 913. The timing controller 913 may be coupled with theheaters controller to control duration of operation of the heaters. Thetiming controller 913 may be coupled with the heaters controller tocontrol timing of the heaters controller selectively activating andselectively deactivating members of the plurality of heaters. The timingcontroller 913 may be coupled with the heaters controller to controlrespective temperatures of respective sensing regions associated withrespective of BAW resonators. The timing controller 913 may be coupledwith the heaters controller 911 to control respective temperatures ofrespective sensing regions to be different from one another. The timingcontroller 913 may be coupled with the heaters controller to controlrespective temperatures of respective sensing regions to controlrespective analyte adsorption at the sensing regions. The timingcontroller 913 is coupled with the heaters controller 911 to controlrespective temperatures of respective sensing regions to controlrespective analyte desorption at the sensing regions. The timingcontroller 913 may be coupled with the heaters controller 911 to varyrespective temperatures of respective sensing regions over time.Respective temperatures of respective sensing regions associated withrespective of BAW resonators of the array 900C may be controlled by thetiming controller 913 coupled with the heaters controller 911, forexample, while the resonant signals receiver 907 coupled with the BAWresonators of the array 900C may receive respective resonant signalstherefrom over time.

The heaters controller 911 may be coupled with the frequency sweepsignals transmitter to control frequency selective power level ofoperation of respective members of the plurality of BAW resonators,e.g., heating of the BAW resonators (e.g., the heating function). Theheaters controller 911 may be coupled with the frequency sweep signalstransmitter to control frequency selective power level transmission torespective members of the plurality of BAW resonators, so as to controlheating of the BAW resonators (e.g., the heating function). The heaterscontroller 911 may be coupled with the frequency sweep signalstransmitter to control frequency selective power level of operation ofrespective members of the plurality of BAW resonators, so as to controltemperature of respective members of the plurality of BAW resonators.The heaters controller 911 may be coupled with the frequency sweepsignals transmitter to control frequency selective power leveltransmission to respective members of the plurality of BAW resonators,so as to control temperature of the BAW resonators.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices formed using the techniques disclosedherein, in accordance with an embodiment of the present disclosure. Asmay be seen, the computing system 1000 houses a motherboard 1002. Themotherboard 1002 may include a number of components, including, but notlimited to, a processor 1004 and at least one communication chip 1006A,1006B each of which may be physically and electrically coupled to themotherboard 1002, or otherwise integrated therein. As will beappreciated, the motherboard 1002 may be, for example, any printedcircuit board, whether a main board, a daughterboard mounted on a mainboard, or the only board of system 1000, etc.

The computing system 1000 may house acoustic resonator sensor arraysystem 1010. Acoustic resonator sensor array system 1010 shown in FIG.10 may be similar to system 9000C shown in FIG. 9C and discussedpreviously herein. Acoustic resonator sensor array system 1010 shown inFIG. 10 may be coupled with a cartridge, e.g., replaceable cartridge1012A. Replaceable cartridge 1012A may be detachably coupled withcartridge receiver 1012B.

Depending on its applications, computing system 1000 may include one ormore other components that may or may not be physically and electricallycoupled to the motherboard 1002. These other components may include, butare not limited to, volatile memory (e.g., DRAM), non-volatile memory(e.g., ROM), a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth). Computing system 1000 may include, or morebroadly, may be associated with Any of the components included incomputing system 1000 may include one or more integrated circuitstructures or devices formed using the disclosed techniques inaccordance with an example embodiment. In some embodiments, multiplefunctions may be integrated into one or more chips (e.g., for instance,note that the communication chips 1006A, 1006B may be part of orotherwise integrated into the processor 1004).

The communication chips 1006A, 1006B enables wireless communications forthe transfer of data to and from the computing system 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chips 1006A, 1006B mayimplement any of a number of wireless standards or protocols, including,but not limited to, Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16family), IEEE 802.20, long term evolution (LTE), Ev− DO, HSPA+, HSDPA+,HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivativesthereof, as well as any other wireless protocols that are designated as3G, 4G, 5G, and beyond. The computing system 1000 may include aplurality of communication chips 1006A, 1006B. For instance, a firstcommunication chip 1006A may be dedicated to shorter range wirelesscommunications such as Wi-Fi and Bluetooth and a second communicationchip 1006B may be dedicated to longer range wireless communications suchas GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, 5G and others. In someembodiments, communication chips 1006A, 1006B may include one or moreacoustic wave devices 1008A, 1008B (e.g., resonators, filters and/oroscillators 1008A, 1008B) as variously described herein (e.g., acousticwave devices including one or more respective stacks of alternating axispiezoelectric material). Acoustic wave devices 1008A, 1008B may beincluded in various ways, e.g., one or more resonators, e.g., one ormore filters, e.g., one or more oscillators. Further, such acoustic wavedevices 1008A, 1008B, e.g., resonators, e.g., filters, e.g., oscillatorsmay be configured to be Super High Frequency (SHF) acoustic wave devices1008A, 1008B or Extremely High Frequency (EHF) acoustic wave devices1008A, 1008B, e.g., resonators, filters, and/or oscillators (e.g.,operating at greater than 3, 4, 5, 6, 7, or 8 GHz, e.g., operating atgreater than 23, 24, 25, 26, 27, 28, 29, or 30 GHz, e.g., operating atgreater than 36, 37, 38, 39, or 40 GHz). Further still, such Super HighFrequency (SHF) acoustic wave devices or Extremely High Frequency (EHF)resonators, filters, and/or oscillators may be included in the RF frontend of computing system 1000 and they may be used for 5G wirelessstandards or protocols, for example. One or more of communication chips1006A, 1006B may be in wireless communication with acoustic resonatorsensor array 1010.

The processor 1004 of the computing system 1000 includes an integratedcircuit die packaged within the processor 1004. In some embodiments, theintegrated circuit die of the processor includes onboard circuitry thatis implemented with one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.The term “processor” may refer to any device or portion of a device thatprocesses, for instance, electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory. Processor 1004 may perform somefunctions of control circuitry of acoustic resonator sensor array system1010.

The communication chips 1006A, 1006B also may include an integratedcircuit die packaged within the communication chips 1006A, 1006B. Inaccordance with some such example embodiments, the integrated circuitdie of the communication chip includes one or more integrated circuitstructures or devices formed using the disclosed techniques as variouslydescribed herein. As will be appreciated in light of this disclosure,note that multi-standard wireless capability may be integrated directlyinto the processor 1004 (e.g., where functionality of any communicationchips 1006A, 1006B is integrated into processor 1004, rather than havingseparate communication chips). Further note that processor 1004 may be achip set having such wireless capability. In short, any number ofprocessor 1004 and/or communication chips 1006A, 1006B may be used.Likewise, any one chip or chip set may have multiple functionsintegrated therein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player, adigital video recorder, or any other electronic device that processesdata or employs one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent. The foregoingdescription of example embodiments has been presented for the purposesof illustration and description. It is not intended to be exhaustive orto limit the present disclosure to the precise forms disclosed. Manymodifications and variations are possible in light of this disclosure.It is intended that the scope of the present disclosure be limited notby this detailed description, but rather by the claims appended hereto.Future filed applications claiming priority to this application mayclaim the disclosed subject matter in a different manner, and maygenerally include any set of one or more limitations as variouslydisclosed or otherwise demonstrated herein.

What is claimed is:
 1. A sensor comprising: a substrate; a Bulk AcousticWave (BAW) resonator arranged over the substrate, the BAW resonatorincluding at least: first and second piezoelectric layers; and a topelectrode; and a sensing region including at least a porousfunctionalized layer to facilitate analysis of an analyte, in which theporous functionalized layer is acoustically coupled with the topelectrode and the second piezoelectric layer.
 2. The sensor in claim 1in which: the first piezoelectric has a first piezoelectric axisorientation; and the second piezoelectric layer has a secondpiezoelectric axis orientation substantially opposing the firstpiezoelectric axis orientation of the first piezoelectric layer.
 3. Thesensor as in claim 1 in which the BAW resonator includes at least athird piezoelectric layer, in which the sensing region including atleast the porous functionalized layer is acoustically coupled with thirdpiezoelectric layer via the top electrode.
 4. The sensor as in claim 3in which the BAW resonator includes at least a fourth piezoelectriclayer, in which the sensing region including at least the porousfunctionalized layer is acoustically coupled with fourth piezoelectriclayer via the top electrode.
 5. The sensor as in claim 4 in which theBAW resonator includes at least an additional pair of piezoelectriclayers, and in which the sensing region including at least the porousfunctionalized layer is acoustically coupled with the additional pair ofpiezoelectric layers via the top electrode.
 6. The sensor in claim 1 inwhich the BAW resonator coupled with the sensing region has a mainresonant frequency in one of a super high frequency band and anextremely high frequency band to facilitate an enhanced sensitivityassociated with the sensing region.
 7. The sensor in claim 1 in whichthe sensor has sufficient sensitivity to detect within a range fromapproximately one half part per million per one hundred attograms toapproximately fifty parts per million per one hundred attograms.
 8. Thesensor in claim 1 in which the sensor has sufficient sensitivity todetect within a range from one KiloHertz CentiMeter Squared per NanoGramto approximately two hundred KiloHertz CentiMeter Squared per NanoGram.9. The sensor as in claim 1 in which the BAW resonator coupled with thesensing region has a quality factor within a range from approximatelythree hundred to approximately fifteen hundred.
 10. The sensor as inclaim 1 in which the sensing region includes at least a nanostructuredregion layer acoustically coupled with the second piezoelectric layer.11. The sensor as in claim 1 in which the porous functionalized layeracoustically coupled with the second piezoelectric layer has a pore sizeto facilitate sensor selectivity of the analyte.
 12. The sensor as inclaim 1 in which the sensing region includes at least a metal-organicframework acoustically coupled with the second piezoelectric layer. 13.The sensor in claim 1 in which the sensing region has a sensing areawithin a range from approximately sixteen hundred square microns toapproximately twenty five thousand six hundred square microns.
 14. Thesensor as in claim 1 comprising a plurality of Bulk Acoustic Wave (BAW)resonators having respective sensing regions in which the plurality ofBAW resonators have respective differing piezoelectric layerthicknesses, to have respective main resonant frequencies that aredifferent from one another, so as to facilitate identification ofrespective members of the plurality of Bulk Acoustic Wave resonators.15. The sensor as in claim 1 comprising a plurality of Bulk AcousticWave (BAW) resonators having respective sensing regions in which therespective sensing regions include at least respective functionalizedlayers that are different from one another to facilitate sensingrespective analytes that are different from one another.
 16. The sensoras in claim 1 comprising a plurality of Bulk Acoustic Wave (BAW)resonators having respective sensing regions in which the respectivesensing regions have sensing areas that are different sizes from oneanother to facilitate respective differing responses.
 17. The sensor asin claim 1 in which the top electrode approximates a harmonic electrodeto facilitate suppressing parasitic lateral resonances.
 18. A sensorcomprising: a substrate; a Bulk Acoustic Wave (BAW) resonator arrangedover the substrate, the BAW resonator comprising a plurality ofpiezoelectric layers; and a sensing region including at least a porousfunctionalized layer having a biological molecule affinity, in which theporous functionalized layer is acoustically coupled with the pluralityof piezoelectric layers.
 19. The sensor as in claim 18 in which theporous functionalized layer has a virus affinity.
 20. The sensor as inclaim 18 in which the porous functionalized layer has a SARS-CoV-2 virusaffinity.
 21. The sensor as in claim 18 in which the sensor hassufficient sensitivity to detect down to a single virus particle in air.22. An acoustic wave device comprising: a substrate; a firstpiezoelectric layer having a first piezoelectric axis orientation; asecond piezoelectric layer acoustically coupled to the firstpiezoelectric layer, the second piezoelectric layer having a secondpiezoelectric axis orientation that is antiparallel to the firstpiezoelectric axis orientation; and a sensing region including at leasta porous functionalized layer acoustically coupled with the secondpiezoelectric layer.
 23. The acoustic wave device of claim 22,comprising a first metal acoustic wave reflector electricallyinterfacing with the first piezoelectric layer, the first metal acousticwave reflector comprising a first pair of metal layers.
 24. The acousticwave device of claim 22, comprising a third piezoelectric layer disposedbetween the first piezoelectric layer and the second piezoelectric layerand being acoustically coupled to the first piezoelectric layer and thesecond piezoelectric layer.
 25. The acoustic wave device of claim 24,comprising a fourth piezoelectric layer disposed between the firstpiezoelectric layer and the second piezoelectric layer and beingacoustically coupled to the first piezoelectric layer and the secondpiezoelectric layer and the third piezoelectric layer.
 26. The acousticwave device of claim 25, comprising an additional pair of piezoelectriclayers disposed between the first piezoelectric layer and the secondpiezoelectric layer and being acoustically coupled to the firstpiezoelectric layer, to the second piezoelectric layer, to thepiezoelectric third layer and to the fourth piezoelectric layer.
 27. Anacoustic wave device comprising: a first plurality of piezoelectriclayers having alternating parallel and antiparallel piezoelectric axisorientations, the first plurality of piezoelectric layers havingrespective thicknesses, the respective thicknesses determining at leastin part a main acoustic resonance frequency of the acoustic wave device;a first metal acoustic wave reflector electrically interfacing with afirst layer of the first plurality of piezoelectric layers; and asensing region including at least a porous functionalized layeracoustically coupled with the first plurality of piezoelectric layers.28. The acoustic wave device of claim 27 comprising a second pluralityof piezoelectric layers having alternating parallel and antiparallelpiezoelectric axis orientations.
 29. The acoustic wave device of claim28 comprising a third plurality of piezoelectric layers havingalternating parallel and antiparallel piezoelectric axis orientations.30. The acoustic wave device of claim 27 in which the main acousticresonance frequency of the acoustic wave device is in one of a superhigh frequency band and an extremely high frequency band.